diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java
index df6da3c7397..b5ff1b07306 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java
@@ -1178,8 +1178,8 @@ public abstract class AbstractJavaCodegen extends DefaultCodegen implements Code
         schema = ModelUtils.getReferencedSchema(this.openAPI, schema);
         if (ModelUtils.isArraySchema(schema)) {
             if (schema.getDefault() == null) {
-                // nullable, optional or containerDefaultToNull set to true
-                if (cp.isNullable || !cp.required || containerDefaultToNull) {
+                // nullable or containerDefaultToNull set to true
+                if (cp.isNullable || containerDefaultToNull) {
                     return null;
                 } else {
                     if (ModelUtils.isSet(schema)) {
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/AbstractJavaCodegenTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/AbstractJavaCodegenTest.java
index 8b6e6281a14..a9a71085f93 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/AbstractJavaCodegenTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/AbstractJavaCodegenTest.java
@@ -605,11 +605,11 @@ public class AbstractJavaCodegenTest {
 
         ModelUtils.setGenerateAliasAsModel(false);
         defaultValue = codegen.toDefaultValue(codegen.fromProperty("", schema), schema);
-        Assert.assertEquals(defaultValue, null);
+        Assert.assertEquals(defaultValue, "new ArrayList<>()");
 
         ModelUtils.setGenerateAliasAsModel(true);
         defaultValue = codegen.toDefaultValue(codegen.fromProperty("", schema), schema);
-        Assert.assertEquals(defaultValue, null);
+        Assert.assertEquals(defaultValue, "new ArrayList<>()");
 
         // Create a map schema with additionalProperties type set to array alias
         schema = new MapSchema().additionalProperties(new Schema().$ref("#/components/schemas/NestedArray"));
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaModelEnumTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaModelEnumTest.java
index ba297ac3fa9..f0c11f141fa 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaModelEnumTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaModelEnumTest.java
@@ -75,7 +75,7 @@ public class JavaModelEnumTest {
         Assert.assertEquals(enumVar.dataType, "List<String>");
         Assert.assertEquals(enumVar.datatypeWithEnum, "List<NameEnum>");
         Assert.assertEquals(enumVar.name, "name");
-        Assert.assertEquals(enumVar.defaultValue, null);
+        Assert.assertEquals(enumVar.defaultValue, "new ArrayList<>()");
         Assert.assertEquals(enumVar.baseType, "List");
         Assert.assertTrue(enumVar.isEnum);
 
@@ -108,7 +108,7 @@ public class JavaModelEnumTest {
         Assert.assertEquals(enumVar.dataType, "List<List<String>>");
         Assert.assertEquals(enumVar.datatypeWithEnum, "List<List<NameEnum>>");
         Assert.assertEquals(enumVar.name, "name");
-        Assert.assertEquals(enumVar.defaultValue, null);
+        Assert.assertEquals(enumVar.defaultValue, "new ArrayList<>()");
         Assert.assertEquals(enumVar.baseType, "List");
         Assert.assertTrue(enumVar.isEnum);
 
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaModelTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaModelTest.java
index 221736e4ea5..e0b97f867df 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaModelTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaModelTest.java
@@ -130,7 +130,7 @@ public class JavaModelTest {
         Assert.assertEquals(property.setter, "setUrls");
         Assert.assertEquals(property.dataType, "List<String>");
         Assert.assertEquals(property.name, "urls");
-        Assert.assertEquals(property.defaultValue, null);
+        Assert.assertEquals(property.defaultValue, "new ArrayList<>()");
         Assert.assertEquals(property.baseType, "List");
         Assert.assertEquals(property.containerType, "array");
         Assert.assertFalse(property.required);
@@ -162,7 +162,7 @@ public class JavaModelTest {
         Assert.assertEquals(property.setter, "setUrls");
         Assert.assertEquals(property.dataType, "Set<String>");
         Assert.assertEquals(property.name, "urls");
-        Assert.assertEquals(property.defaultValue, null);
+        Assert.assertEquals(property.defaultValue, "new LinkedHashSet<>()");
         Assert.assertEquals(property.baseType, "Set");
         Assert.assertEquals(property.containerType, "set");
         Assert.assertFalse(property.required);
@@ -248,7 +248,7 @@ public class JavaModelTest {
         Assert.assertEquals(property.setter, "setList2D");
         Assert.assertEquals(property.dataType, "List<List<Pet>>");
         Assert.assertEquals(property.name, "list2D");
-        Assert.assertEquals(property.defaultValue, null);
+        Assert.assertEquals(property.defaultValue, "new ArrayList<>()");
         Assert.assertEquals(property.baseType, "List");
         Assert.assertEquals(property.containerType, "array");
         Assert.assertFalse(property.required);
@@ -333,7 +333,7 @@ public class JavaModelTest {
         Assert.assertEquals(property.setter, "setChildren");
         Assert.assertEquals(property.dataType, "List<Children>");
         Assert.assertEquals(property.name, "children");
-        Assert.assertEquals(property.defaultValue, null);
+        Assert.assertEquals(property.defaultValue, "new ArrayList<>()");
         Assert.assertEquals(property.baseType, "List");
         Assert.assertEquals(property.containerType, "array");
         Assert.assertFalse(property.required);
@@ -396,7 +396,7 @@ public class JavaModelTest {
         Assert.assertEquals(property.setter, "setChildren");
         Assert.assertEquals(property.dataType, "List<Children>");
         Assert.assertEquals(property.name, "children");
-        Assert.assertEquals(property.defaultValue, null);
+        Assert.assertEquals(property.defaultValue, "new ArrayList<>()");
         Assert.assertEquals(property.baseType, "List");
         Assert.assertEquals(property.containerType, "array");
         Assert.assertFalse(property.required);
@@ -429,7 +429,7 @@ public class JavaModelTest {
         Assert.assertEquals(property.setter, "setChildren");
         Assert.assertEquals(property.dataType, "Set<Children>");
         Assert.assertEquals(property.name, "children");
-        Assert.assertEquals(property.defaultValue, null);
+        Assert.assertEquals(property.defaultValue, "new LinkedHashSet<>()");
         Assert.assertEquals(property.baseType, "Set");
         Assert.assertEquals(property.containerType, "set");
         Assert.assertFalse(property.required);
@@ -466,7 +466,7 @@ public class JavaModelTest {
         Assert.assertEquals(property.setter, "setChildren");
         Assert.assertEquals(property.dataType, "List<Child>");
         Assert.assertEquals(property.name, "children");
-        Assert.assertEquals(property.defaultValue, null);
+        Assert.assertEquals(property.defaultValue, "new ArrayList<>()");
         Assert.assertEquals(property.baseType, "List");
         Assert.assertEquals(property.containerType, "array");
         Assert.assertFalse(property.required);
@@ -974,7 +974,7 @@ public class JavaModelTest {
         Assert.assertEquals(property2.setter, "setArray");
         Assert.assertEquals(property2.dataType, "List<String>");
         Assert.assertEquals(property2.name, "array");
-        Assert.assertEquals(property2.defaultValue, null);
+        Assert.assertEquals(property2.defaultValue, "new ArrayList<>()");
         Assert.assertEquals(property2.baseType, "List");
         Assert.assertTrue(property2.isContainer);
         Assert.assertTrue(property2.isXmlWrapped);
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/spring/SpringCodegenTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/spring/SpringCodegenTest.java
index c88416c2259..a00a999b078 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/spring/SpringCodegenTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/spring/SpringCodegenTest.java
@@ -4518,4 +4518,34 @@ public class SpringCodegenTest {
                 .assertMethod("equals")
         ;
     }
+
+    @Test
+    public void optionalListShouldBeEmpty() throws IOException {
+        File output = Files.createTempDirectory("test").toFile().getCanonicalFile();
+        output.deleteOnExit();
+
+        OpenAPI openAPI = new OpenAPIParser()
+                .readLocation("src/test/resources/3_1/petstore.yaml", null, new ParseOptions()).getOpenAPI();
+        SpringCodegen codegen = new SpringCodegen();
+        codegen.setLibrary(SPRING_CLOUD_LIBRARY);
+        codegen.setOutputDir(output.getAbsolutePath());
+        codegen.additionalProperties().put(CodegenConstants.MODEL_PACKAGE, "xyz.model");
+        codegen.additionalProperties().put(CodegenConstants.API_NAME_SUFFIX, "Controller");
+        codegen.additionalProperties().put(CodegenConstants.API_PACKAGE, "xyz.controller");
+        codegen.additionalProperties().put(CodegenConstants.MODEL_NAME_SUFFIX, "Dto");
+
+
+        ClientOptInput input = new ClientOptInput()
+                .openAPI(openAPI)
+                .config(codegen);
+
+        DefaultGenerator generator = new DefaultGenerator();
+        Map<String, File> files = generator.opts(input).generate().stream()
+                .collect(Collectors.toMap(File::getName, Function.identity()));
+
+        JavaFileAssert.assertThat(files.get("PetDto.java"))
+                .fileContains("private List<@Valid TagDto> tags = new ArrayList<>();")
+                .fileContains("private List<String> photoUrls = new ArrayList<>();");
+
+    }
 }
diff --git a/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/DefaultValue.java b/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/DefaultValue.java
index 7cc23db2aa6..d487a67a821 100644
--- a/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/DefaultValue.java
+++ b/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/DefaultValue.java
@@ -99,7 +99,7 @@ public class DefaultValue {
   private List<Integer> arrayIntegerDefault = new ArrayList<>(Arrays.asList(1, 3));
 
   public static final String JSON_PROPERTY_ARRAY_STRING = "array_string";
-  private List<String> arrayString;
+  private List<String> arrayString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_STRING_NULLABLE = "array_string_nullable";
   private JsonNullable<List<String>> arrayStringNullable = JsonNullable.<List<String>>undefined();
diff --git a/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/Pet.java
index 0410f0af40d..1b71752b064 100644
--- a/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/Pet.java
@@ -57,7 +57,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java b/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java
index bac04c88cef..be1941bef8f 100644
--- a/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java
+++ b/samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java
@@ -39,7 +39,7 @@ import java.util.StringJoiner;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter {
   public static final String JSON_PROPERTY_VALUES = "values";
-  private List<String> values;
+  private List<String> values = new ArrayList<>();
 
   public TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter() {
   }
diff --git a/samples/client/echo_api/java/apache-httpclient/src/test/java/org/openapitools/client/CustomTest.java b/samples/client/echo_api/java/apache-httpclient/src/test/java/org/openapitools/client/CustomTest.java
index ecb8c5b6605..7e0076c7e6a 100644
--- a/samples/client/echo_api/java/apache-httpclient/src/test/java/org/openapitools/client/CustomTest.java
+++ b/samples/client/echo_api/java/apache-httpclient/src/test/java/org/openapitools/client/CustomTest.java
@@ -13,258 +13,273 @@
 
 package org.openapitools.client;
 
-import com.fasterxml.jackson.core.type.TypeReference;
-import org.junit.Assert;
-import org.openapitools.client.ApiException;
-import org.openapitools.client.api.*;
-import org.openapitools.client.model.*;
-import org.junit.Test;
-import org.junit.Ignore;
-
 import java.io.IOException;
-import java.util.*;
+import java.util.Arrays;
+import java.util.Collections;
 
+import org.junit.Assert;
+import org.junit.Test;
+import org.openapitools.client.api.BodyApi;
+import org.openapitools.client.api.QueryApi;
+import org.openapitools.client.model.Category;
+import org.openapitools.client.model.DataQuery;
+import org.openapitools.client.model.DefaultValue;
+import org.openapitools.client.model.Pet;
+import org.openapitools.client.model.Query;
+import org.openapitools.client.model.StringEnumRef;
+import org.openapitools.client.model.TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter;
+
+import com.fasterxml.jackson.core.type.TypeReference;
 
 /**
  * API tests for QueryApi
  */
 public class CustomTest {
 
-    private final QueryApi api = new QueryApi();
-    private final BodyApi bodyApi = new BodyApi();
+   private final QueryApi api = new QueryApi();
+   private final BodyApi bodyApi = new BodyApi();
 
-    /**
-     * Test body parameter(s)
-     * <p>
-     * Test body parameter(s)
-     *
-     * @throws ApiException if the Api call fails
-     */
-    @Test
-    public void testEchoBodyPet() throws ApiException {
-        Pet queryObject = new Pet().id(12345L).name("Hello World").
-                photoUrls(Arrays.asList(new String[]{"http://a.com", "http://b.com"})).category(new Category().id(987L).name("new category"));
+   /**
+    * Test body parameter(s)
+    * <p>
+    * Test body parameter(s)
+    *
+    * @throws ApiException if the Api call fails
+    */
+   @Test
+   public void testEchoBodyPet() throws ApiException {
+      final Pet queryObject = new Pet().id( 12345L ).name( "Hello World" ).
+            photoUrls( Arrays.asList( new String[] { "http://a.com", "http://b.com" } ) ).category( new Category().id( 987L ).name( "new category" ) );
 
-        Pet p = bodyApi.testEchoBodyPet(queryObject);
-        Assert.assertNotNull(p);
-        Assert.assertEquals("Hello World", p.getName());
-        Assert.assertEquals(Long.valueOf(12345L), p.getId());
+      final Pet p = bodyApi.testEchoBodyPet( queryObject );
+      Assert.assertNotNull( p );
+      Assert.assertEquals( "Hello World", p.getName() );
+      Assert.assertEquals( Long.valueOf( 12345L ), p.getId() );
 
-        // response is empty body
-        Pet p2 = bodyApi.testEchoBodyPet(null);
-        Assert.assertNull(p2);
-    }
+      // response is empty body
+      final Pet p2 = bodyApi.testEchoBodyPet( null );
+      Assert.assertNull( p2 );
+   }
 
-    /**
-     * Test body parameter(s)
-     * <p>
-     * Test body parameter(s)
-     *
-     * @throws ApiException if the Api call fails
-     */
-    @Test
-    public void testEchoBodyPetResponseString() throws ApiException {
-        // response is empty body
-        String p2 = bodyApi.testEchoBodyPetResponseString(null);
-        Assert.assertNull(p2);
-    }
+   /**
+    * Test body parameter(s)
+    * <p>
+    * Test body parameter(s)
+    *
+    * @throws ApiException if the Api call fails
+    */
+   @Test
+   public void testEchoBodyPetResponseString() throws ApiException {
+      // response is empty body
+      final String p2 = bodyApi.testEchoBodyPetResponseString( null );
+      Assert.assertNull( p2 );
+   }
 
-    /**
-     * Test query parameter(s)
-     * <p>
-     * Test query parameter(s)
-     *
-     * @throws ApiException if the Api call fails
-     */
-    @Test
-    public void testQueryStyleFormExplodeTrueObjectTest() throws ApiException {
-        Pet queryObject = new Pet().id(12345L).name("Hello World").
-                photoUrls(Arrays.asList(new String[]{"http://a.com", "http://b.com"})).category(new Category().id(987L).name("new category"));
+   /**
+    * Test query parameter(s)
+    * <p>
+    * Test query parameter(s)
+    *
+    * @throws ApiException if the Api call fails
+    */
+   @Test
+   public void testQueryStyleFormExplodeTrueObjectTest() throws ApiException {
+      final Pet queryObject = new Pet().id( 12345L ).name( "Hello World" ).
+            photoUrls( Arrays.asList( new String[] { "http://a.com", "http://b.com" } ) ).category( new Category().id( 987L ).name( "new category" ) );
 
-        String response = api.testQueryStyleFormExplodeTrueObject(queryObject);
-        org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser(response);
-        Assert.assertEquals("/query/style_form/explode_true/object?id=12345&name=Hello%20World&category=class%20Category%20%7B%0A%20%20%20%20id%3A%20987%0A%20%20%20%20name%3A%20new%20category%0A%7D&photoUrls=http%3A%2F%2Fa.com&photoUrls=http%3A%2F%2Fb.com", p.path);
-    }
+      final String response = api.testQueryStyleFormExplodeTrueObject( queryObject );
+      final org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser( response );
+      Assert.assertEquals(
+            "/query/style_form/explode_true/object?id=12345&name=Hello%20World&category=class%20Category%20%7B%0A%20%20%20%20id%3A%20987%0A%20%20%20%20name%3A%20new%20category%0A%7D&photoUrls=http%3A%2F%2Fa.com&photoUrls=http%3A%2F%2Fb.com",
+            p.path );
+   }
 
-    /**
-     * Test query parameter(s)
-     * <p>
-     * Test query parameter(s)
-     *
-     * @throws ApiException if the Api call fails
-     */
-    @Test
-    public void testQueryStyleDeepObjectExplodeTrueObject() throws ApiException {
-        Pet queryObject = new Pet().id(12345L).name("Hello World").
-                photoUrls(Arrays.asList(new String[]{"http://a.com", "http://b.com"})).category(new Category().id(987L).name("new category"));
+   /**
+    * Test query parameter(s)
+    * <p>
+    * Test query parameter(s)
+    *
+    * @throws ApiException if the Api call fails
+    */
+   @Test
+   public void testQueryStyleDeepObjectExplodeTrueObject() throws ApiException {
+      final Pet queryObject = new Pet().id( 12345L ).name( "Hello World" ).
+            photoUrls( Arrays.asList( new String[] { "http://a.com", "http://b.com" } ) ).category( new Category().id( 987L ).name( "new category" ) );
 
-        Assert.assertEquals("query_object[id]=12345&query_object[name]=Hello%20World&query_object[category][id]=987&query_object[category][name]=new%20category&query_object[photoUrls][0]=http%3A%2F%2Fa.com&query_object[photoUrls][1]=http%3A%2F%2Fb.com", queryObject.toUrlQueryString("query_object"));
+      Assert.assertEquals(
+            "query_object[id]=12345&query_object[name]=Hello%20World&query_object[category][id]=987&query_object[category][name]=new%20category&query_object[photoUrls][0]=http%3A%2F%2Fa.com&query_object[photoUrls][1]=http%3A%2F%2Fb.com",
+            queryObject.toUrlQueryString( "query_object" ) );
 
-        String response = api.testQueryStyleDeepObjectExplodeTrueObject(queryObject);
-        org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser(response);
-        Assert.assertEquals("/query/style_deepObject/explode_true/object?query_object[id]=12345&query_object[name]=Hello%20World&query_object[category][id]=987&query_object[category][name]=new%20category&query_object[photoUrls][0]=http%3A%2F%2Fa.com&query_object[photoUrls][1]=http%3A%2F%2Fb.com", p.path);
-    }
+      final String response = api.testQueryStyleDeepObjectExplodeTrueObject( queryObject );
+      final org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser( response );
+      Assert.assertEquals(
+            "/query/style_deepObject/explode_true/object?query_object[id]=12345&query_object[name]=Hello%20World&query_object[category][id]=987&query_object[category][name]=new%20category&query_object[photoUrls][0]=http%3A%2F%2Fa.com&query_object[photoUrls][1]=http%3A%2F%2Fb.com",
+            p.path );
+   }
 
-    /**
-     * Test query parameter(s)
-     * <p>
-     * Test query parameter(s)
-     *
-     * @throws ApiException if the Api call fails
-     */
-    @Test
-    public void testQueryStyleFormExplodeTrueObjectAllOfTest() throws ApiException {
-        DataQuery queryObject = new DataQuery().text("Hello World");
-        queryObject.setId(3487L);
-        queryObject.setOutcomes(Arrays.asList(Query.OutcomesEnum.SKIPPED, Query.OutcomesEnum.FAILURE));
+   /**
+    * Test query parameter(s)
+    * <p>
+    * Test query parameter(s)
+    *
+    * @throws ApiException if the Api call fails
+    */
+   @Test
+   public void testQueryStyleFormExplodeTrueObjectAllOfTest() throws ApiException {
+      final DataQuery queryObject = new DataQuery().text( "Hello World" );
+      queryObject.setId( 3487L );
+      queryObject.setOutcomes( Arrays.asList( Query.OutcomesEnum.SKIPPED, Query.OutcomesEnum.FAILURE ) );
 
-        String response = api.testQueryStyleFormExplodeTrueObjectAllOf(queryObject);
-        org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser(response);
-        Assert.assertEquals("/query/style_form/explode_true/object/allOf?id=3487&outcomes=SKIPPED&outcomes=FAILURE&text=Hello%20World", p.path);
-    }
+      final String response = api.testQueryStyleFormExplodeTrueObjectAllOf( queryObject );
+      final org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser( response );
+      Assert.assertEquals( "/query/style_form/explode_true/object/allOf?id=3487&outcomes=SKIPPED&outcomes=FAILURE&text=Hello%20World", p.path );
+   }
 
-    /**
-     * Test query parameter(s)
-     * <p>
-     * Test query parameter(s)
-     *
-     * @throws ApiException if the Api call fails
-     */
-    @Test
-    public void testQueryStyleFormExplodeTrueArrayString() throws ApiException {
-        TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter q = new TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter()
-                .values(Arrays.asList(new String[]{"hello world 1", "hello world 2"}));
+   /**
+    * Test query parameter(s)
+    * <p>
+    * Test query parameter(s)
+    *
+    * @throws ApiException if the Api call fails
+    */
+   @Test
+   public void testQueryStyleFormExplodeTrueArrayString() throws ApiException {
+      final TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter q = new TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter()
+            .values( Arrays.asList( new String[] { "hello world 1", "hello world 2" } ) );
 
-        String response = api.testQueryStyleFormExplodeTrueArrayString(q);
-        org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser(response);
-        Assert.assertEquals("/query/style_form/explode_true/array_string?values=hello%20world%201&values=hello%20world%202", p.path);
-    }
+      final String response = api.testQueryStyleFormExplodeTrueArrayString( q );
+      final org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser( response );
+      Assert.assertEquals( "/query/style_form/explode_true/array_string?values=hello%20world%201&values=hello%20world%202", p.path );
+   }
 
-    /**
-     * Test query parameter(s)
-     * <p>
-     * Test query parameter(s)
-     *
-     * @throws ApiException if the Api call fails
-     */
-    @Test
-    public void testQueryIntegerBooleanString() throws ApiException {
-        String response = api.testQueryIntegerBooleanString(1, true, "Hello World");
-        org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser(response);
-        Assert.assertEquals("/query/integer/boolean/string?integer_query=1&boolean_query=true&string_query=Hello%20World", p.path);
-    }
+   /**
+    * Test query parameter(s)
+    * <p>
+    * Test query parameter(s)
+    *
+    * @throws ApiException if the Api call fails
+    */
+   @Test
+   public void testQueryIntegerBooleanString() throws ApiException {
+      final String response = api.testQueryIntegerBooleanString( 1, true, "Hello World" );
+      final org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser( response );
+      Assert.assertEquals( "/query/integer/boolean/string?integer_query=1&boolean_query=true&string_query=Hello%20World", p.path );
+   }
 
-    @Test
-    public void testArrayDefaultValues() {
-        // test array default values
-        DefaultValue d = new DefaultValue();
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().size(), 2);
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().get(0), StringEnumRef.SUCCESS);
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().get(1), StringEnumRef.FAILURE);
+   @Test
+   public void testArrayDefaultValues() {
+      // test array default values
+      final DefaultValue d = new DefaultValue();
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().get( 0 ), StringEnumRef.SUCCESS );
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().get( 1 ), StringEnumRef.FAILURE );
 
-        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 2);
-        Assert.assertEquals(d.getArrayStringEnumDefault().get(0), DefaultValue.ArrayStringEnumDefaultEnum.SUCCESS);
-        Assert.assertEquals(d.getArrayStringEnumDefault().get(1), DefaultValue.ArrayStringEnumDefaultEnum.FAILURE);
+      Assert.assertEquals( d.getArrayStringEnumDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayStringEnumDefault().get( 0 ), DefaultValue.ArrayStringEnumDefaultEnum.SUCCESS );
+      Assert.assertEquals( d.getArrayStringEnumDefault().get( 1 ), DefaultValue.ArrayStringEnumDefaultEnum.FAILURE );
 
-        Assert.assertEquals(d.getArrayStringDefault().size(), 2);
-        Assert.assertEquals(d.getArrayStringDefault().get(0), "failure");
-        Assert.assertEquals(d.getArrayStringDefault().get(1), "skipped");
+      Assert.assertEquals( d.getArrayStringDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayStringDefault().get( 0 ), "failure" );
+      Assert.assertEquals( d.getArrayStringDefault().get( 1 ), "skipped" );
 
-        Assert.assertEquals(d.getArrayIntegerDefault().size(), 2);
-        Assert.assertEquals(d.getArrayIntegerDefault().get(0), Integer.valueOf(1));
-        Assert.assertEquals(d.getArrayIntegerDefault().get(1), Integer.valueOf(3));
+      Assert.assertEquals( d.getArrayIntegerDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayIntegerDefault().get( 0 ), Integer.valueOf( 1 ) );
+      Assert.assertEquals( d.getArrayIntegerDefault().get( 1 ), Integer.valueOf( 3 ) );
 
-        Assert.assertNull(d.getArrayStringNullable());
-        Assert.assertNull(d.getArrayString());
+      Assert.assertNull( d.getArrayStringNullable() );
+      Assert.assertEquals( d.getArrayString(), Collections.emptyList() );
 
-        // test addItem
-        d.addArrayStringEnumDefaultItem(DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED);
-        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 3);
-        Assert.assertEquals(d.getArrayStringEnumDefault().get(2), DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED);
+      // test addItem
+      d.addArrayStringEnumDefaultItem( DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED );
+      Assert.assertEquals( d.getArrayStringEnumDefault().size(), 3 );
+      Assert.assertEquals( d.getArrayStringEnumDefault().get( 2 ), DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED );
 
-        d.addArrayStringDefaultItem("new item");
-        Assert.assertEquals(d.getArrayStringDefault().size(), 3);
-        Assert.assertEquals(d.getArrayStringDefault().get(2), "new item");
+      d.addArrayStringDefaultItem( "new item" );
+      Assert.assertEquals( d.getArrayStringDefault().size(), 3 );
+      Assert.assertEquals( d.getArrayStringDefault().get( 2 ), "new item" );
 
-        d.addArrayIntegerDefaultItem(5);
-        Assert.assertEquals(d.getArrayIntegerDefault().size(), 3);
-        Assert.assertEquals(d.getArrayIntegerDefault().get(2), Integer.valueOf(5));
+      d.addArrayIntegerDefaultItem( 5 );
+      Assert.assertEquals( d.getArrayIntegerDefault().size(), 3 );
+      Assert.assertEquals( d.getArrayIntegerDefault().get( 2 ), Integer.valueOf( 5 ) );
 
-    }
+   }
 
-    @Test
-    public void testDefaultValuesSerializationWithEmptyPayload() throws IOException {
-        ApiClient apiClient = new ApiClient();
+   @Test
+   public void testDefaultValuesSerializationWithEmptyPayload() throws IOException {
+      final ApiClient apiClient = new ApiClient();
 
-        String str = "{}";
+      final String str = "{}";
 
-        DefaultValue d = apiClient.getObjectMapper().readValue(str, new TypeReference<DefaultValue>() {
-        });
+      final DefaultValue d = apiClient.getObjectMapper().readValue( str, new TypeReference<DefaultValue>() {
+      } );
 
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().size(), 2);
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().get(0), StringEnumRef.SUCCESS);
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().get(1), StringEnumRef.FAILURE);
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().get( 0 ), StringEnumRef.SUCCESS );
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().get( 1 ), StringEnumRef.FAILURE );
 
-        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 2);
-        Assert.assertEquals(d.getArrayStringEnumDefault().get(0), DefaultValue.ArrayStringEnumDefaultEnum.SUCCESS);
-        Assert.assertEquals(d.getArrayStringEnumDefault().get(1), DefaultValue.ArrayStringEnumDefaultEnum.FAILURE);
+      Assert.assertEquals( d.getArrayStringEnumDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayStringEnumDefault().get( 0 ), DefaultValue.ArrayStringEnumDefaultEnum.SUCCESS );
+      Assert.assertEquals( d.getArrayStringEnumDefault().get( 1 ), DefaultValue.ArrayStringEnumDefaultEnum.FAILURE );
 
-        Assert.assertEquals(d.getArrayStringDefault().size(), 2);
-        Assert.assertEquals(d.getArrayStringDefault().get(0), "failure");
-        Assert.assertEquals(d.getArrayStringDefault().get(1), "skipped");
+      Assert.assertEquals( d.getArrayStringDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayStringDefault().get( 0 ), "failure" );
+      Assert.assertEquals( d.getArrayStringDefault().get( 1 ), "skipped" );
 
-        Assert.assertEquals(d.getArrayIntegerDefault().size(), 2);
-        Assert.assertEquals(d.getArrayIntegerDefault().get(0), Integer.valueOf(1));
-        Assert.assertEquals(d.getArrayIntegerDefault().get(1), Integer.valueOf(3));
+      Assert.assertEquals( d.getArrayIntegerDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayIntegerDefault().get( 0 ), Integer.valueOf( 1 ) );
+      Assert.assertEquals( d.getArrayIntegerDefault().get( 1 ), Integer.valueOf( 3 ) );
 
-        Assert.assertNull(d.getArrayStringNullable());
-        Assert.assertNull(d.getArrayString());
+      Assert.assertNull( d.getArrayStringNullable() );
+      Assert.assertEquals( d.getArrayString(), Collections.emptyList() );
 
-        Assert.assertEquals(apiClient.getObjectMapper().writeValueAsString(d), "{\"array_string_enum_ref_default\":[\"success\",\"failure\"],\"array_string_enum_default\":[\"success\",\"failure\"],\"array_string_default\":[\"failure\",\"skipped\"],\"array_integer_default\":[1,3]}");
-    }
+      Assert.assertEquals( apiClient.getObjectMapper().writeValueAsString( d ),
+            "{\"array_string_enum_ref_default\":[\"success\",\"failure\"],\"array_string_enum_default\":[\"success\",\"failure\"],\"array_string_default\":[\"failure\",\"skipped\"],\"array_integer_default\":[1,3],\"array_string\":[]}" );
+   }
 
-    @Test
-    public void testDefaultValuesSerializationWithJSONString() throws IOException {
-        ApiClient apiClient = new ApiClient();
+   @Test
+   public void testDefaultValuesSerializationWithJSONString() throws IOException {
+      final ApiClient apiClient = new ApiClient();
 
-        String str = "{ \"array_string_enum_ref_default\": [\"unclassified\"], \"array_string_enum_default\": [\"unclassified\"], \"array_string_default\": [\"failure\"] }";
+      final String str = "{ \"array_string_enum_ref_default\": [\"unclassified\"], \"array_string_enum_default\": [\"unclassified\"], \"array_string_default\": [\"failure\"] }";
 
-        DefaultValue d = apiClient.getObjectMapper().readValue(str, new TypeReference<DefaultValue>() {
-        });
+      final DefaultValue d = apiClient.getObjectMapper().readValue( str, new TypeReference<DefaultValue>() {
+      } );
 
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().size(), 1);
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().get(0), StringEnumRef.UNCLASSIFIED);
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().size(), 1 );
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().get( 0 ), StringEnumRef.UNCLASSIFIED );
 
-        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 1);
-        Assert.assertEquals(d.getArrayStringEnumDefault().get(0), DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED);
+      Assert.assertEquals( d.getArrayStringEnumDefault().size(), 1 );
+      Assert.assertEquals( d.getArrayStringEnumDefault().get( 0 ), DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED );
 
-        Assert.assertEquals(d.getArrayStringDefault().size(), 1);
-        Assert.assertEquals(d.getArrayStringDefault().get(0), "failure");
+      Assert.assertEquals( d.getArrayStringDefault().size(), 1 );
+      Assert.assertEquals( d.getArrayStringDefault().get( 0 ), "failure" );
 
-        Assert.assertEquals(d.getArrayIntegerDefault().size(), 2);
-        Assert.assertEquals(d.getArrayIntegerDefault().get(0), Integer.valueOf(1));
-        Assert.assertEquals(d.getArrayIntegerDefault().get(1), Integer.valueOf(3));
+      Assert.assertEquals( d.getArrayIntegerDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayIntegerDefault().get( 0 ), Integer.valueOf( 1 ) );
+      Assert.assertEquals( d.getArrayIntegerDefault().get( 1 ), Integer.valueOf( 3 ) );
 
-        Assert.assertNull(d.getArrayStringNullable());
-        Assert.assertNull(d.getArrayString());
+      Assert.assertNull( d.getArrayStringNullable() );
+      Assert.assertEquals( d.getArrayString(), Collections.emptyList() );
 
-        Assert.assertEquals(apiClient.getObjectMapper().writeValueAsString(d), "{\"array_string_enum_ref_default\":[\"unclassified\"],\"array_string_enum_default\":[\"unclassified\"],\"array_string_default\":[\"failure\"],\"array_integer_default\":[1,3]}");
-    }
+      Assert.assertEquals( apiClient.getObjectMapper().writeValueAsString( d ),
+            "{\"array_string_enum_ref_default\":[\"unclassified\"],\"array_string_enum_default\":[\"unclassified\"],\"array_string_default\":[\"failure\"],\"array_integer_default\":[1,3],\"array_string\":[]}" );
+   }
 
-    @Test
-    public void testDefaultValuesSerializationWithIncorrectDefaultValues() throws IOException {
-        ApiClient apiClient = new ApiClient();
+   @Test
+   public void testDefaultValuesSerializationWithIncorrectDefaultValues() throws IOException {
+      final ApiClient apiClient = new ApiClient();
 
-        String str = "{ \"array_string_enum_default\": [\"invalid\"] }";
+      final String str = "{ \"array_string_enum_default\": [\"invalid\"] }";
 
-        try {
-            DefaultValue d = apiClient.getObjectMapper().readValue(str, new TypeReference<DefaultValue>() {
-            });
-            Assert.assertTrue(false); // the test should not reach this line
-        } catch (com.fasterxml.jackson.databind.exc.ValueInstantiationException e) {
-            Assert.assertEquals(e.getMessage(), "Cannot construct instance of `org.openapitools.client.model.DefaultValue$ArrayStringEnumDefaultEnum`, problem: Unexpected value 'invalid'\n" +
-                    " at [Source: (String)\"{ \"array_string_enum_default\": [\"invalid\"] }\"; line: 1, column: 33] (through reference chain: org.openapitools.client.model.DefaultValue[\"array_string_enum_default\"]->java.util.ArrayList[0])");
-        }
-    }
+      try {
+         final DefaultValue d = apiClient.getObjectMapper().readValue( str, new TypeReference<DefaultValue>() {
+         } );
+         Assert.assertTrue( false ); // the test should not reach this line
+      } catch ( final com.fasterxml.jackson.databind.exc.ValueInstantiationException e ) {
+         Assert.assertEquals( e.getMessage(),
+               "Cannot construct instance of `org.openapitools.client.model.DefaultValue$ArrayStringEnumDefaultEnum`, problem: Unexpected value 'invalid'\n" +
+                     " at [Source: (String)\"{ \"array_string_enum_default\": [\"invalid\"] }\"; line: 1, column: 33] (through reference chain: org.openapitools.client.model.DefaultValue[\"array_string_enum_default\"]->java.util.ArrayList[0])" );
+      }
+   }
 
 }
diff --git a/samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/DefaultValue.java b/samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/DefaultValue.java
index 2e0caf16884..26c76c80bad 100644
--- a/samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/DefaultValue.java
+++ b/samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/DefaultValue.java
@@ -99,7 +99,7 @@ public class DefaultValue {
 
   public static final String SERIALIZED_NAME_ARRAY_STRING = "array_string";
   @SerializedName(SERIALIZED_NAME_ARRAY_STRING)
-  private List<String> arrayString;
+  private List<String> arrayString = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_STRING_NULLABLE = "array_string_nullable";
   @SerializedName(SERIALIZED_NAME_ARRAY_STRING_NULLABLE)
diff --git a/samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/Pet.java
index 7328799a8c9..3d94f1a7929 100644
--- a/samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/Pet.java
@@ -50,7 +50,7 @@ public class Pet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java b/samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java
index e55b9d4bc6b..7e547a32a77 100644
--- a/samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java
+++ b/samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java
@@ -32,7 +32,7 @@ import java.util.List;
 public class TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter {
   public static final String SERIALIZED_NAME_VALUES = "values";
   @SerializedName(SERIALIZED_NAME_VALUES)
-  private List<String> values;
+  private List<String> values = new ArrayList<>();
 
   public TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter() {
   }
diff --git a/samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/DefaultValue.java b/samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/DefaultValue.java
index 1850876f836..20b4faa06e8 100644
--- a/samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/DefaultValue.java
+++ b/samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/DefaultValue.java
@@ -100,7 +100,7 @@ public class DefaultValue {
   private List<Integer> arrayIntegerDefault = new ArrayList<>(Arrays.asList(1, 3));
 
   public static final String JSON_PROPERTY_ARRAY_STRING = "array_string";
-  private List<String> arrayString;
+  private List<String> arrayString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_STRING_NULLABLE = "array_string_nullable";
   private JsonNullable<List<String>> arrayStringNullable = JsonNullable.<List<String>>undefined();
diff --git a/samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/Pet.java
index 0ed7180d0f1..4d7f82de0cc 100644
--- a/samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/Pet.java
@@ -58,7 +58,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java b/samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java
index ca6578480f2..f57663d4b33 100644
--- a/samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java
+++ b/samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java
@@ -39,7 +39,7 @@ import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter {
   public static final String JSON_PROPERTY_VALUES = "values";
-  private List<String> values;
+  private List<String> values = new ArrayList<>();
 
   public TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter() { 
   }
diff --git a/samples/client/echo_api/java/native/src/test/java/org/openapitools/client/CustomTest.java b/samples/client/echo_api/java/native/src/test/java/org/openapitools/client/CustomTest.java
index 0eb53fa61b1..0b2a52f9434 100644
--- a/samples/client/echo_api/java/native/src/test/java/org/openapitools/client/CustomTest.java
+++ b/samples/client/echo_api/java/native/src/test/java/org/openapitools/client/CustomTest.java
@@ -13,337 +13,359 @@
 
 package org.openapitools.client;
 
-import com.fasterxml.jackson.core.type.TypeReference;
-import org.junit.Assert;
-import org.openapitools.client.ApiException;
-import org.openapitools.client.api.*;
-import org.openapitools.client.model.*;
-import org.junit.Test;
-import org.junit.Ignore;
-
 import java.io.BufferedWriter;
 import java.io.File;
 import java.io.FileWriter;
 import java.io.IOException;
 import java.nio.file.Files;
-import java.util.*;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Objects;
+
+import org.junit.Assert;
+import org.junit.Test;
+import org.openapitools.client.api.BodyApi;
+import org.openapitools.client.api.FormApi;
+import org.openapitools.client.api.QueryApi;
+import org.openapitools.client.model.Category;
+import org.openapitools.client.model.DataQuery;
+import org.openapitools.client.model.DefaultValue;
+import org.openapitools.client.model.Pet;
+import org.openapitools.client.model.Query;
+import org.openapitools.client.model.StringEnumRef;
+import org.openapitools.client.model.TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter;
+import org.openapitools.client.model.TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter;
+
+import com.fasterxml.jackson.core.type.TypeReference;
 
 /**
  * API tests for QueryApi
  */
 public class CustomTest {
 
-    private final QueryApi api = new QueryApi();
-    private final BodyApi bodyApi = new BodyApi();
-    private final FormApi formApi = new FormApi();
+   private final QueryApi api = new QueryApi();
+   private final BodyApi bodyApi = new BodyApi();
+   private final FormApi formApi = new FormApi();
 
+   /**
+    * Test body parameter(s)
+    * <p>
+    * Test body parameter(s)
+    *
+    * @throws ApiException if the Api call fails
+    */
+   @Test
+   public void testEchoBodyPet() throws ApiException {
+      final Pet queryObject = new Pet().id( 12345L ).name( "Hello World" ).
+            photoUrls( Arrays.asList( new String[] { "http://a.com", "http://b.com" } ) ).category( new Category().id( 987L ).name( "new category" ) );
 
-    /**
-     * Test body parameter(s)
-     * <p>
-     * Test body parameter(s)
-     *
-     * @throws ApiException if the Api call fails
-     */
-    @Test
-    public void testEchoBodyPet() throws ApiException {
-        Pet queryObject = new Pet().id(12345L).name("Hello World").
-                photoUrls(Arrays.asList(new String[]{"http://a.com", "http://b.com"})).category(new Category().id(987L).name("new category"));
+      final Pet p = bodyApi.testEchoBodyPet( queryObject );
+      Assert.assertNotNull( p );
+      Assert.assertEquals( "Hello World", p.getName() );
+      Assert.assertEquals( Long.valueOf( 12345L ), p.getId() );
 
-        Pet p = bodyApi.testEchoBodyPet(queryObject);
-        Assert.assertNotNull(p);
-        Assert.assertEquals("Hello World", p.getName());
-        Assert.assertEquals(Long.valueOf(12345L), p.getId());
+      // response is empty body
+      final Pet p2 = bodyApi.testEchoBodyPet( null );
+      Assert.assertNull( p2 );
+   }
 
-        // response is empty body
-        Pet p2 = bodyApi.testEchoBodyPet(null);
-        Assert.assertNull(p2);
-    }
+   /**
+    * Test allOf body parameter(s)
+    * <p>
+    * Test allOf body parameter(s)
+    *
+    * @throws ApiException if the Api call fails
+    */
+   @Test
+   public void testEchoBodyAllOfPet() throws ApiException {
+      final Pet queryObject = new Pet().id( 12345L ).name( "Hello World" ).
+            photoUrls( Arrays.asList( new String[] { "http://a.com", "http://b.com" } ) ).category( new Category().id( 987L ).name( "new category" ) );
 
-    /**
-     * Test allOf body parameter(s)
-     * <p>
-     * Test allOf body parameter(s)
-     *
-     * @throws ApiException if the Api call fails
-     */
-    @Test
-    public void testEchoBodyAllOfPet() throws ApiException {
-        Pet queryObject = new Pet().id(12345L).name("Hello World").
-                photoUrls(Arrays.asList(new String[]{"http://a.com", "http://b.com"})).category(new Category().id(987L).name("new category"));
+      final Pet p = bodyApi.testEchoBodyAllOfPet( queryObject );
+      Assert.assertNotNull( p );
+      Assert.assertEquals( "Hello World", p.getName() );
+      Assert.assertEquals( Long.valueOf( 12345L ), p.getId() );
 
-        Pet p = bodyApi.testEchoBodyAllOfPet(queryObject);
-        Assert.assertNotNull(p);
-        Assert.assertEquals("Hello World", p.getName());
-        Assert.assertEquals(Long.valueOf(12345L), p.getId());
+      // response is empty body
+      final Pet p2 = bodyApi.testEchoBodyPet( null );
+      Assert.assertNull( p2 );
+   }
 
-        // response is empty body
-        Pet p2 = bodyApi.testEchoBodyPet(null);
-        Assert.assertNull(p2);
-    }
+   /**
+    * Test query parameter(s)
+    * <p>
+    * Test query parameter(s)
+    *
+    * @throws ApiException if the Api call fails
+    */
+   @Test
+   public void testQueryStyleFormExplodeTrueObjectTest() throws ApiException {
+      final Pet queryObject = new Pet().id( 12345L ).name( "Hello World" ).
+            photoUrls( Arrays.asList( new String[] { "http://a.com", "http://b.com" } ) ).category( new Category().id( 987L ).name( "new category" ) );
 
-    /**
-     * Test query parameter(s)
-     * <p>
-     * Test query parameter(s)
-     *
-     * @throws ApiException if the Api call fails
-     */
-    @Test
-    public void testQueryStyleFormExplodeTrueObjectTest() throws ApiException {
-        Pet queryObject = new Pet().id(12345L).name("Hello World").
-                photoUrls(Arrays.asList(new String[]{"http://a.com", "http://b.com"})).category(new Category().id(987L).name("new category"));
+      final String response = api.testQueryStyleFormExplodeTrueObject( queryObject );
+      final org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser( response );
+      Assert.assertEquals(
+            "/query/style_form/explode_true/object?id=12345&name=Hello%20World&category=class%20Category%20%7B%0A%20%20%20%20id%3A%20987%0A%20%20%20%20name%3A%20new%20category%0A%7D&photoUrls=http%3A%2F%2Fa.com&photoUrls=http%3A%2F%2Fb.com",
+            p.path );
+   }
 
-        String response = api.testQueryStyleFormExplodeTrueObject(queryObject);
-        org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser(response);
-        Assert.assertEquals("/query/style_form/explode_true/object?id=12345&name=Hello%20World&category=class%20Category%20%7B%0A%20%20%20%20id%3A%20987%0A%20%20%20%20name%3A%20new%20category%0A%7D&photoUrls=http%3A%2F%2Fa.com&photoUrls=http%3A%2F%2Fb.com", p.path);
-    }
+   /**
+    * Test query parameter(s)
+    * <p>
+    * Test query parameter(s)
+    *
+    * @throws ApiException if the Api call fails
+    */
+   @Test
+   public void testQueryStyleFormExplodeTrueObjectAllOfTest() throws ApiException {
+      final DataQuery queryObject = new DataQuery().text( "Hello World" );
+      queryObject.setId( 3487L );
+      queryObject.setOutcomes( Arrays.asList( Query.OutcomesEnum.SKIPPED, Query.OutcomesEnum.FAILURE ) );
 
-    /**
-     * Test query parameter(s)
-     * <p>
-     * Test query parameter(s)
-     *
-     * @throws ApiException if the Api call fails
-     */
-    @Test
-    public void testQueryStyleFormExplodeTrueObjectAllOfTest() throws ApiException {
-        DataQuery queryObject = new DataQuery().text("Hello World");
-        queryObject.setId(3487L);
-        queryObject.setOutcomes(Arrays.asList(Query.OutcomesEnum.SKIPPED, Query.OutcomesEnum.FAILURE));
+      final String response = api.testQueryStyleFormExplodeTrueObjectAllOf( queryObject );
+      final org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser( response );
+      Assert.assertEquals( "/query/style_form/explode_true/object/allOf?id=3487&outcomes=SKIPPED&outcomes=FAILURE&text=Hello%20World", p.path );
+   }
 
-        String response = api.testQueryStyleFormExplodeTrueObjectAllOf(queryObject);
-        org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser(response);
-        Assert.assertEquals("/query/style_form/explode_true/object/allOf?id=3487&outcomes=SKIPPED&outcomes=FAILURE&text=Hello%20World", p.path);
-    }
+   /**
+    * Test query parameter(s)
+    * <p>
+    * Test query parameter(s)
+    *
+    * @throws ApiException if the Api call fails
+    */
+   @Test
+   public void testQueryStyleDeepObjectExplodeTrueObject() throws ApiException {
+      final Pet queryObject = new Pet().id( 12345L ).name( "Hello World" ).
+            photoUrls( Arrays.asList( new String[] { "http://a.com", "http://b.com" } ) ).category( new Category().id( 987L ).name( "new category" ) );
 
-    /**
-     * Test query parameter(s)
-     * <p>
-     * Test query parameter(s)
-     *
-     * @throws ApiException if the Api call fails
-     */
-    @Test
-    public void testQueryStyleDeepObjectExplodeTrueObject() throws ApiException {
-        Pet queryObject = new Pet().id(12345L).name("Hello World").
-                photoUrls(Arrays.asList(new String[]{"http://a.com", "http://b.com"})).category(new Category().id(987L).name("new category"));
+      Assert.assertEquals(
+            "query_object[id]=12345&query_object[name]=Hello%20World&query_object[category][id]=987&query_object[category][name]=new%20category&query_object[photoUrls][0]=http%3A%2F%2Fa.com&query_object[photoUrls][1]=http%3A%2F%2Fb.com",
+            queryObject.toUrlQueryString( "query_object" ) );
 
-        Assert.assertEquals("query_object[id]=12345&query_object[name]=Hello%20World&query_object[category][id]=987&query_object[category][name]=new%20category&query_object[photoUrls][0]=http%3A%2F%2Fa.com&query_object[photoUrls][1]=http%3A%2F%2Fb.com", queryObject.toUrlQueryString("query_object"));
+      final String response = api.testQueryStyleDeepObjectExplodeTrueObject( queryObject );
+      final org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser( response );
+      Assert.assertEquals(
+            "/query/style_deepObject/explode_true/object?query_object[id]=12345&query_object[name]=Hello%20World&query_object[category][id]=987&query_object[category][name]=new%20category&query_object[photoUrls][0]=http%3A%2F%2Fa.com&query_object[photoUrls][1]=http%3A%2F%2Fb.com",
+            p.path );
+   }
 
-        String response = api.testQueryStyleDeepObjectExplodeTrueObject(queryObject);
-        org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser(response);
-        Assert.assertEquals("/query/style_deepObject/explode_true/object?query_object[id]=12345&query_object[name]=Hello%20World&query_object[category][id]=987&query_object[category][name]=new%20category&query_object[photoUrls][0]=http%3A%2F%2Fa.com&query_object[photoUrls][1]=http%3A%2F%2Fb.com", p.path);
-    }
+   /**
+    * Test query parameter(s)
+    * <p>
+    * Test query parameter(s)
+    *
+    * @throws ApiException if the Api call fails
+    */
+   @Test
+   public void testQueryStyleDeepObjectExplodeTrueObjectAllOf() throws ApiException {
+      final TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter queryObject = new TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter().id(
+                  12345L ).name( "Hello World" ).
+            color( "red" ).size( "small" );
 
-    /**
-     * Test query parameter(s)
-     * <p>
-     * Test query parameter(s)
-     *
-     * @throws ApiException if the Api call fails
-     */
-    @Test
-    public void testQueryStyleDeepObjectExplodeTrueObjectAllOf() throws ApiException {
-        TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter queryObject = new TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter().id(12345L).name("Hello World").
-                color("red").size("small");
+      Assert.assertEquals( "query_object[size]=small&query_object[color]=red&query_object[id]=12345&query_object[name]=Hello%20World",
+            queryObject.toUrlQueryString( "query_object" ) );
 
-        Assert.assertEquals("query_object[size]=small&query_object[color]=red&query_object[id]=12345&query_object[name]=Hello%20World", queryObject.toUrlQueryString("query_object"));
+      final String response = api.testQueryStyleDeepObjectExplodeTrueObjectAllOf( queryObject );
+      final org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser( response );
+      Assert.assertEquals(
+            "/query/style_deepObject/explode_true/object/allOf?query_object[size]=small&query_object[color]=red&query_object[id]=12345&query_object[name]=Hello%20World",
+            p.path );
+   }
 
-        String response = api.testQueryStyleDeepObjectExplodeTrueObjectAllOf(queryObject);
-        org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser(response);
-        Assert.assertEquals("/query/style_deepObject/explode_true/object/allOf?query_object[size]=small&query_object[color]=red&query_object[id]=12345&query_object[name]=Hello%20World", p.path);
-    }
+   /**
+    * Test query parameter(s)
+    * <p>
+    * Test query parameter(s)
+    *
+    * @throws ApiException if the Api call fails
+    */
+   @Test
+   public void testQueryStyleFormExplodeTrueArrayString() throws ApiException {
+      final TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter q = new TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter()
+            .values( Arrays.asList( new String[] { "hello world 1", "hello world 2" } ) );
 
-    /**
-     * Test query parameter(s)
-     * <p>
-     * Test query parameter(s)
-     *
-     * @throws ApiException if the Api call fails
-     */
-    @Test
-    public void testQueryStyleFormExplodeTrueArrayString() throws ApiException {
-        TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter q = new TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter()
-                .values(Arrays.asList(new String[]{"hello world 1", "hello world 2"}));
+      final String response = api.testQueryStyleFormExplodeTrueArrayString( q );
+      final org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser( response );
+      Assert.assertEquals( "/query/style_form/explode_true/array_string?values=hello%20world%201&values=hello%20world%202", p.path );
+   }
 
-        String response = api.testQueryStyleFormExplodeTrueArrayString(q);
-        org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser(response);
-        Assert.assertEquals("/query/style_form/explode_true/array_string?values=hello%20world%201&values=hello%20world%202", p.path);
-    }
+   @Test
+   public void testArrayDefaultValues() {
+      // test array default values
+      final DefaultValue d = new DefaultValue();
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().get( 0 ), StringEnumRef.SUCCESS );
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().get( 1 ), StringEnumRef.FAILURE );
 
-    @Test
-    public void testArrayDefaultValues() {
-        // test array default values
-        DefaultValue d = new DefaultValue();
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().size(), 2);
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().get(0), StringEnumRef.SUCCESS);
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().get(1), StringEnumRef.FAILURE);
+      Assert.assertEquals( d.getArrayStringEnumDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayStringEnumDefault().get( 0 ), DefaultValue.ArrayStringEnumDefaultEnum.SUCCESS );
+      Assert.assertEquals( d.getArrayStringEnumDefault().get( 1 ), DefaultValue.ArrayStringEnumDefaultEnum.FAILURE );
 
-        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 2);
-        Assert.assertEquals(d.getArrayStringEnumDefault().get(0), DefaultValue.ArrayStringEnumDefaultEnum.SUCCESS);
-        Assert.assertEquals(d.getArrayStringEnumDefault().get(1), DefaultValue.ArrayStringEnumDefaultEnum.FAILURE);
+      Assert.assertEquals( d.getArrayStringDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayStringDefault().get( 0 ), "failure" );
+      Assert.assertEquals( d.getArrayStringDefault().get( 1 ), "skipped" );
 
-        Assert.assertEquals(d.getArrayStringDefault().size(), 2);
-        Assert.assertEquals(d.getArrayStringDefault().get(0), "failure");
-        Assert.assertEquals(d.getArrayStringDefault().get(1), "skipped");
+      Assert.assertEquals( d.getArrayIntegerDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayIntegerDefault().get( 0 ), Integer.valueOf( 1 ) );
+      Assert.assertEquals( d.getArrayIntegerDefault().get( 1 ), Integer.valueOf( 3 ) );
 
-        Assert.assertEquals(d.getArrayIntegerDefault().size(), 2);
-        Assert.assertEquals(d.getArrayIntegerDefault().get(0), Integer.valueOf(1));
-        Assert.assertEquals(d.getArrayIntegerDefault().get(1), Integer.valueOf(3));
+      Assert.assertNull( d.getArrayStringNullable() );
+      Assert.assertNull( d.getArrayStringExtensionNullable() );
+      Assert.assertEquals( d.getArrayString(), List.of() );
 
-        Assert.assertNull(d.getArrayStringNullable());
-        Assert.assertNull(d.getArrayStringExtensionNullable());
-        Assert.assertNull(d.getArrayString());
+      // test addItem
+      d.addArrayStringEnumDefaultItem( DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED );
+      Assert.assertEquals( d.getArrayStringEnumDefault().size(), 3 );
+      Assert.assertEquals( d.getArrayStringEnumDefault().get( 2 ), DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED );
 
-        // test addItem
-        d.addArrayStringEnumDefaultItem(DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED);
-        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 3);
-        Assert.assertEquals(d.getArrayStringEnumDefault().get(2), DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED);
+      d.addArrayStringDefaultItem( "new item" );
+      Assert.assertEquals( d.getArrayStringDefault().size(), 3 );
+      Assert.assertEquals( d.getArrayStringDefault().get( 2 ), "new item" );
 
-        d.addArrayStringDefaultItem("new item");
-        Assert.assertEquals(d.getArrayStringDefault().size(), 3);
-        Assert.assertEquals(d.getArrayStringDefault().get(2), "new item");
+      d.addArrayIntegerDefaultItem( 5 );
+      Assert.assertEquals( d.getArrayIntegerDefault().size(), 3 );
+      Assert.assertEquals( d.getArrayIntegerDefault().get( 2 ), Integer.valueOf( 5 ) );
+   }
 
-        d.addArrayIntegerDefaultItem(5);
-        Assert.assertEquals(d.getArrayIntegerDefault().size(), 3);
-        Assert.assertEquals(d.getArrayIntegerDefault().get(2), Integer.valueOf(5));
-    }
+   @Test
+   public void testDefaultValuesSerializationWithEmptyPayload() throws IOException {
+      final ApiClient apiClient = new ApiClient();
 
-    @Test
-    public void testDefaultValuesSerializationWithEmptyPayload() throws IOException {
-        ApiClient apiClient = new ApiClient();
+      final String str = "{}";
 
-        String str = "{}";
+      final DefaultValue d = apiClient.getObjectMapper().readValue( str, new TypeReference<>() {
+      } );
 
-        DefaultValue d = apiClient.getObjectMapper().readValue(str, new TypeReference<DefaultValue>() {
-        });
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().get( 0 ), StringEnumRef.SUCCESS );
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().get( 1 ), StringEnumRef.FAILURE );
 
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().size(), 2);
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().get(0), StringEnumRef.SUCCESS);
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().get(1), StringEnumRef.FAILURE);
+      Assert.assertEquals( d.getArrayStringEnumDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayStringEnumDefault().get( 0 ), DefaultValue.ArrayStringEnumDefaultEnum.SUCCESS );
+      Assert.assertEquals( d.getArrayStringEnumDefault().get( 1 ), DefaultValue.ArrayStringEnumDefaultEnum.FAILURE );
 
-        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 2);
-        Assert.assertEquals(d.getArrayStringEnumDefault().get(0), DefaultValue.ArrayStringEnumDefaultEnum.SUCCESS);
-        Assert.assertEquals(d.getArrayStringEnumDefault().get(1), DefaultValue.ArrayStringEnumDefaultEnum.FAILURE);
+      Assert.assertEquals( d.getArrayStringDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayStringDefault().get( 0 ), "failure" );
+      Assert.assertEquals( d.getArrayStringDefault().get( 1 ), "skipped" );
 
-        Assert.assertEquals(d.getArrayStringDefault().size(), 2);
-        Assert.assertEquals(d.getArrayStringDefault().get(0), "failure");
-        Assert.assertEquals(d.getArrayStringDefault().get(1), "skipped");
+      Assert.assertEquals( d.getArrayIntegerDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayIntegerDefault().get( 0 ), Integer.valueOf( 1 ) );
+      Assert.assertEquals( d.getArrayIntegerDefault().get( 1 ), Integer.valueOf( 3 ) );
 
-        Assert.assertEquals(d.getArrayIntegerDefault().size(), 2);
-        Assert.assertEquals(d.getArrayIntegerDefault().get(0), Integer.valueOf(1));
-        Assert.assertEquals(d.getArrayIntegerDefault().get(1), Integer.valueOf(3));
+      Assert.assertNull( d.getArrayStringNullable() );
+      Assert.assertNull( d.getArrayStringExtensionNullable() );
+      Assert.assertEquals( d.getArrayString(), List.of() );
 
-        Assert.assertNull(d.getArrayStringNullable());
-        Assert.assertNull(d.getArrayStringExtensionNullable());
-        Assert.assertNull(d.getArrayString());
+      Assert.assertEquals( apiClient.getObjectMapper().writeValueAsString( d ),
+            "{\"array_string_enum_ref_default\":[\"success\",\"failure\"],\"array_string_enum_default\":[\"success\",\"failure\"],\"array_string_default\":[\"failure\",\"skipped\"],\"array_integer_default\":[1,3],\"array_string\":[]}" );
+   }
 
-        Assert.assertEquals(apiClient.getObjectMapper().writeValueAsString(d), "{\"array_string_enum_ref_default\":[\"success\",\"failure\"],\"array_string_enum_default\":[\"success\",\"failure\"],\"array_string_default\":[\"failure\",\"skipped\"],\"array_integer_default\":[1,3]}");
-    }
+   @Test
+   public void testDefaultValuesSerializationWithJSONString() throws IOException {
+      final ApiClient apiClient = new ApiClient();
 
-    @Test
-    public void testDefaultValuesSerializationWithJSONString() throws IOException {
-        ApiClient apiClient = new ApiClient();
+      final String str = "{ \"array_string_enum_ref_default\": [\"unclassified\"], \"array_string_enum_default\": [\"unclassified\"], \"array_string_default\": [\"failure\"] }";
 
-        String str = "{ \"array_string_enum_ref_default\": [\"unclassified\"], \"array_string_enum_default\": [\"unclassified\"], \"array_string_default\": [\"failure\"] }";
+      final DefaultValue d = apiClient.getObjectMapper().readValue( str, new TypeReference<>() {
+      } );
 
-        DefaultValue d = apiClient.getObjectMapper().readValue(str, new TypeReference<DefaultValue>() {
-        });
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().size(), 1 );
+      Assert.assertEquals( d.getArrayStringEnumRefDefault().get( 0 ), StringEnumRef.UNCLASSIFIED );
 
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().size(), 1);
-        Assert.assertEquals(d.getArrayStringEnumRefDefault().get(0), StringEnumRef.UNCLASSIFIED);
+      Assert.assertEquals( d.getArrayStringEnumDefault().size(), 1 );
+      Assert.assertEquals( d.getArrayStringEnumDefault().get( 0 ), DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED );
 
-        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 1);
-        Assert.assertEquals(d.getArrayStringEnumDefault().get(0), DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED);
+      Assert.assertEquals( d.getArrayStringDefault().size(), 1 );
+      Assert.assertEquals( d.getArrayStringDefault().get( 0 ), "failure" );
 
-        Assert.assertEquals(d.getArrayStringDefault().size(), 1);
-        Assert.assertEquals(d.getArrayStringDefault().get(0), "failure");
+      Assert.assertEquals( d.getArrayIntegerDefault().size(), 2 );
+      Assert.assertEquals( d.getArrayIntegerDefault().get( 0 ), Integer.valueOf( 1 ) );
+      Assert.assertEquals( d.getArrayIntegerDefault().get( 1 ), Integer.valueOf( 3 ) );
 
-        Assert.assertEquals(d.getArrayIntegerDefault().size(), 2);
-        Assert.assertEquals(d.getArrayIntegerDefault().get(0), Integer.valueOf(1));
-        Assert.assertEquals(d.getArrayIntegerDefault().get(1), Integer.valueOf(3));
+      Assert.assertNull( d.getArrayStringNullable() );
+      Assert.assertNull( d.getArrayStringExtensionNullable() );
+      Assert.assertEquals( d.getArrayString(), List.of() );
 
-        Assert.assertNull(d.getArrayStringNullable());
-        Assert.assertNull(d.getArrayStringExtensionNullable());
-        Assert.assertNull(d.getArrayString());
+      Assert.assertEquals( apiClient.getObjectMapper().writeValueAsString( d ),
+            "{\"array_string_enum_ref_default\":[\"unclassified\"],\"array_string_enum_default\":[\"unclassified\"],\"array_string_default\":[\"failure\"],\"array_integer_default\":[1,3],\"array_string\":[]}" );
+   }
 
-        Assert.assertEquals(apiClient.getObjectMapper().writeValueAsString(d), "{\"array_string_enum_ref_default\":[\"unclassified\"],\"array_string_enum_default\":[\"unclassified\"],\"array_string_default\":[\"failure\"],\"array_integer_default\":[1,3]}");
-    }
+   @Test
+   public void testDefaultValuesSerializationWithIncorrectDefaultValues() throws IOException {
+      final ApiClient apiClient = new ApiClient();
 
-    @Test
-    public void testDefaultValuesSerializationWithIncorrectDefaultValues() throws IOException {
-        ApiClient apiClient = new ApiClient();
+      final String str = "{ \"array_string_enum_default\": [\"invalid\"] }";
 
-        String str = "{ \"array_string_enum_default\": [\"invalid\"] }";
+      try {
+         final DefaultValue d = apiClient.getObjectMapper().readValue( str, new TypeReference<>() {
+         } );
+         Assert.assertTrue( false ); // the test should not reach this line
+      } catch ( final com.fasterxml.jackson.databind.exc.ValueInstantiationException e ) {
+         Assert.assertEquals( e.getMessage(),
+               "Cannot construct instance of `org.openapitools.client.model.DefaultValue$ArrayStringEnumDefaultEnum`, problem: Unexpected value 'invalid'\n" +
+                     " at [Source: (String)\"{ \"array_string_enum_default\": [\"invalid\"] }\"; line: 1, column: 33] (through reference chain: org.openapitools.client.model.DefaultValue[\"array_string_enum_default\"]->java.util.ArrayList[0])" );
+      }
+   }
 
-        try {
-            DefaultValue d = apiClient.getObjectMapper().readValue(str, new TypeReference<DefaultValue>() {
-            });
-            Assert.assertTrue(false); // the test should not reach this line
-        } catch (com.fasterxml.jackson.databind.exc.ValueInstantiationException e) {
-            Assert.assertEquals(e.getMessage(), "Cannot construct instance of `org.openapitools.client.model.DefaultValue$ArrayStringEnumDefaultEnum`, problem: Unexpected value 'invalid'\n" +
-                    " at [Source: (String)\"{ \"array_string_enum_default\": [\"invalid\"] }\"; line: 1, column: 33] (through reference chain: org.openapitools.client.model.DefaultValue[\"array_string_enum_default\"]->java.util.ArrayList[0])");
-        }
-    }
+   /**
+    * Test form parameter(s)
+    *
+    * Test form parameter(s)
+    *
+    * @throws ApiException
+    *          if the Api call fails
+    */
+   @Test
+   public void testFormIntegerBooleanStringTest() throws ApiException {
+      final Integer integerForm = 1337;
+      final Boolean booleanForm = true;
+      final String stringForm = "Hello World";
+      final String response = formApi.testFormIntegerBooleanString( integerForm, booleanForm, stringForm );
+      final org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser( response );
+      Assert.assertEquals( "/form/integer/boolean/string", p.path );
+      Assert.assertEquals( "3b\ninteger_form=1337&boolean_form=true&string_form=Hello+World\n0\n\n", p.body );
+   }
 
-    /**
-     * Test form parameter(s)
-     *
-     * Test form parameter(s)
-     *
-     * @throws ApiException
-     *          if the Api call fails
-     */
-    @Test
-    public void testFormIntegerBooleanStringTest() throws ApiException {
-        Integer integerForm = 1337;
-        Boolean booleanForm = true;
-        String stringForm = "Hello World";
-        String response = formApi.testFormIntegerBooleanString(integerForm, booleanForm, stringForm);
-        org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser(response);
-        Assert.assertEquals("/form/integer/boolean/string", p.path);
-        Assert.assertEquals("3b\ninteger_form=1337&boolean_form=true&string_form=Hello+World\n0\n\n", p.body);
-    }
+   @Test
+   public void testFormOneOf() throws ApiException {
+      final String form1 = "form1_example"; // String |
+      final Integer form2 = 56; // Integer |
+      final String form3 = "form3  example"; // String |
+      final Boolean form4 = true;
+      final String response = formApi.testFormOneof( form1, form2, form3, form4, null, null );
+      final org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser( response );
+      Assert.assertEquals( "/form/oneof", p.path );
+      Assert.assertEquals( "3c\nform1=form1_example&form2=56&form3=form3++example&form4=true\n0\n\n", p.body );
+   }
 
-    @Test
-    public void testFormOneOf() throws ApiException {
-        String form1 = "form1_example"; // String | 
-        Integer form2 = 56; // Integer | 
-        String form3 = "form3  example"; // String | 
-        Boolean form4 = true;
-        String response = formApi.testFormOneof(form1, form2, form3, form4, null, null);
-        org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser(response);
-        Assert.assertEquals("/form/oneof", p.path);
-        Assert.assertEquals("3c\nform1=form1_example&form2=56&form3=form3++example&form4=true\n0\n\n", p.body);
-    }
+   @Test
+   public void testBodyMultipartFormdataArrayOfBinary() throws ApiException {
+      final File file1 = Objects.requireNonNull( getFile( "Hello" ) );
+      final File file2 = Objects.requireNonNull( getFile( "World" ) );
 
-    @Test
-    public void testBodyMultipartFormdataArrayOfBinary() throws ApiException {
-        File file1 = Objects.requireNonNull(getFile("Hello"));
-        File file2 = Objects.requireNonNull(getFile("World"));
+      final String response = bodyApi.testBodyMultipartFormdataArrayOfBinary( List.of( file1, file2 ) );
+      final org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser( response );
 
-        String response = bodyApi.testBodyMultipartFormdataArrayOfBinary(List.of(file1, file2));
-        org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser(response);
+      Assert.assertEquals( "/body/application/octetstream/array_of_binary", p.path );
 
-        Assert.assertEquals("/body/application/octetstream/array_of_binary", p.path);
+      Assert.assertTrue( p.body.contains( file1.getName() ) );
+      Assert.assertTrue( p.body.contains( "Hello" ) );
+      Assert.assertTrue( p.body.contains( file2.getName() ) );
+      Assert.assertTrue( p.body.contains( "World" ) );
+   }
 
-        Assert.assertTrue(p.body.contains(file1.getName()));
-        Assert.assertTrue(p.body.contains("Hello"));
-        Assert.assertTrue(p.body.contains(file2.getName()));
-        Assert.assertTrue(p.body.contains("World"));
-    }
+   private File getFile( final String content ) {
+      try {
+         final File tempFile = Files.createTempFile( "tempFile", ".txt" ).toFile();
+         final BufferedWriter writer = new BufferedWriter( new FileWriter( tempFile ) );
+         writer.write( content );
+         writer.close();
 
-    private File getFile(String content) {
-        try {
-            File tempFile = Files.createTempFile("tempFile", ".txt").toFile();
-            BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile));
-            writer.write(content);
-            writer.close();
-
-            return tempFile;
-        } catch (IOException e) {
-            return null;
-        }
-    }
+         return tempFile;
+      } catch ( final IOException e ) {
+         return null;
+      }
+   }
 }
diff --git a/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/model/DefaultValue.java b/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/model/DefaultValue.java
index 7ecc7ef300c..7a89a302359 100644
--- a/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/model/DefaultValue.java
+++ b/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/model/DefaultValue.java
@@ -127,7 +127,7 @@ public class DefaultValue {
 
   public static final String SERIALIZED_NAME_ARRAY_STRING = "array_string";
   @SerializedName(SERIALIZED_NAME_ARRAY_STRING)
-  private List<String> arrayString;
+  private List<String> arrayString = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_STRING_NULLABLE = "array_string_nullable";
   @SerializedName(SERIALIZED_NAME_ARRAY_STRING_NULLABLE)
diff --git a/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/model/Pet.java
index ad1fd968e34..a8a082a9495 100644
--- a/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/model/Pet.java
@@ -73,7 +73,7 @@ public class Pet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java b/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java
index 0985f58679f..973df714229 100644
--- a/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java
+++ b/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java
@@ -55,7 +55,7 @@ import org.openapitools.client.JSON;
 public class TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter {
   public static final String SERIALIZED_NAME_VALUES = "values";
   @SerializedName(SERIALIZED_NAME_VALUES)
-  private List<String> values;
+  private List<String> values = new ArrayList<>();
 
   public TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter() {
   }
diff --git a/samples/client/echo_api/java/resteasy/src/main/java/org/openapitools/client/model/DefaultValue.java b/samples/client/echo_api/java/resteasy/src/main/java/org/openapitools/client/model/DefaultValue.java
index 4f499f71796..526dc2dabdd 100644
--- a/samples/client/echo_api/java/resteasy/src/main/java/org/openapitools/client/model/DefaultValue.java
+++ b/samples/client/echo_api/java/resteasy/src/main/java/org/openapitools/client/model/DefaultValue.java
@@ -96,7 +96,7 @@ public class DefaultValue {
   private List<Integer> arrayIntegerDefault = new ArrayList<>(Arrays.asList(1, 3));
 
   public static final String JSON_PROPERTY_ARRAY_STRING = "array_string";
-  private List<String> arrayString;
+  private List<String> arrayString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_STRING_NULLABLE = "array_string_nullable";
   private JsonNullable<List<String>> arrayStringNullable = JsonNullable.<List<String>>undefined();
diff --git a/samples/client/echo_api/java/resteasy/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/echo_api/java/resteasy/src/main/java/org/openapitools/client/model/Pet.java
index b9bb1b98c9e..2aa25f45437 100644
--- a/samples/client/echo_api/java/resteasy/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/echo_api/java/resteasy/src/main/java/org/openapitools/client/model/Pet.java
@@ -54,7 +54,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/echo_api/java/resteasy/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java b/samples/client/echo_api/java/resteasy/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java
index 77e8319586e..38c98272e8a 100644
--- a/samples/client/echo_api/java/resteasy/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java
+++ b/samples/client/echo_api/java/resteasy/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java
@@ -36,7 +36,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter {
   public static final String JSON_PROPERTY_VALUES = "values";
-  private List<String> values;
+  private List<String> values = new ArrayList<>();
 
   public TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter() {
   }
diff --git a/samples/client/petstore/groovy/src/main/groovy/org/openapitools/model/Pet.groovy b/samples/client/petstore/groovy/src/main/groovy/org/openapitools/model/Pet.groovy
index 5fd22bc10d5..1ca93fb46c9 100644
--- a/samples/client/petstore/groovy/src/main/groovy/org/openapitools/model/Pet.groovy
+++ b/samples/client/petstore/groovy/src/main/groovy/org/openapitools/model/Pet.groovy
@@ -19,7 +19,7 @@ class Pet {
     
     List<String> photoUrls = new ArrayList<>()
     
-    List<Tag> tags
+    List<Tag> tags = new ArrayList<>()
 
     enum StatusEnum {
     
diff --git a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index 854544e3267..a6251b6a257 100644
--- a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -39,7 +39,7 @@ import java.util.StringJoiner;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 75f8107a179..f4b5b0a453a 100644
--- a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -39,7 +39,7 @@ import java.util.StringJoiner;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ArrayTest.java
index d3f8d747b84..ebc3cdc1855 100644
--- a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -41,13 +41,13 @@ import java.util.StringJoiner;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/EnumArrays.java
index 7d3eaaff4d4..6bf7090b67e 100644
--- a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -112,7 +112,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index 02514927fc6..1ee4f1f9b33 100644
--- a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -43,7 +43,7 @@ public class FileSchemaTestClass {
   private ModelFile _file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/NullableClass.java b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/NullableClass.java
index bc8a2831bea..796fbb1bcc9 100644
--- a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/NullableClass.java
+++ b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/NullableClass.java
@@ -82,7 +82,7 @@ public class NullableClass extends HashMap<String, Object> {
   private JsonNullable<List<Object>> arrayAndItemsNullableProp = JsonNullable.<List<Object>>undefined();
 
   public static final String JSON_PROPERTY_ARRAY_ITEMS_NULLABLE = "array_items_nullable";
-  private List<Object> arrayItemsNullable;
+  private List<Object> arrayItemsNullable = new ArrayList<>();
 
   public static final String JSON_PROPERTY_OBJECT_NULLABLE_PROP = "object_nullable_prop";
   private JsonNullable<Map<String, Object>> objectNullableProp = JsonNullable.<Map<String, Object>>undefined();
diff --git a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
index ccd21d43d93..f4e68367362 100644
--- a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
+++ b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
@@ -52,7 +52,7 @@ public class ObjectWithDeprecatedFields {
   private DeprecatedObject deprecatedRef;
 
   public static final String JSON_PROPERTY_BARS = "bars";
-  private List<String> bars;
+  private List<String> bars = new ArrayList<>();
 
   public ObjectWithDeprecatedFields() {
   }
diff --git a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/Pet.java
index 181badeb4f5..bc9c7d4dadc 100644
--- a/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/apache-httpclient/src/main/java/org/openapitools/client/model/Pet.java
@@ -60,7 +60,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index b5f41d83322..7d11f92dcc4 100644
--- a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -37,7 +37,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 0e602ec377f..3b9d7c3bf67 100644
--- a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -37,7 +37,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/ArrayTest.java
index d7d52870664..be60bd5687a 100644
--- a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -39,13 +39,13 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/EnumArrays.java
index b6a10195296..d3666e41a49 100644
--- a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -110,7 +110,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index bf0c7447774..44de80a34b5 100644
--- a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -41,7 +41,7 @@ public class FileSchemaTestClass {
   private File file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<File> files;
+  private List<File> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/Pet.java
index 67cfb90f56e..45609c414c5 100644
--- a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/Pet.java
@@ -58,7 +58,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/XmlItem.java b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/XmlItem.java
index 15356867733..102dfa4cb93 100644
--- a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/XmlItem.java
+++ b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/model/XmlItem.java
@@ -77,7 +77,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   public static final String JSON_PROPERTY_WRAPPED_ARRAY = "wrapped_array";
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_STRING = "name_string";
   private String nameString;
@@ -92,10 +92,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   public static final String JSON_PROPERTY_NAME_ARRAY = "name_array";
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_WRAPPED_ARRAY = "name_wrapped_array";
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_STRING = "prefix_string";
   private String prefixString;
@@ -110,10 +110,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   public static final String JSON_PROPERTY_PREFIX_ARRAY = "prefix_array";
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_STRING = "namespace_string";
   private String namespaceString;
@@ -128,10 +128,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   public static final String JSON_PROPERTY_NAMESPACE_ARRAY = "namespace_array";
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_STRING = "prefix_ns_string";
   private String prefixNsString;
@@ -146,10 +146,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   public static final String JSON_PROPERTY_PREFIX_NS_ARRAY = "prefix_ns_array";
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem() {
   }
diff --git a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index 9ff76c17092..da012a34175 100644
--- a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 4237f9900dc..abbba5d0f0d 100644
--- a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ArrayTest.java
index 31f8ae83b9b..766a62dd175 100644
--- a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -38,13 +38,13 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/EnumArrays.java
index c67f0f8f4d6..fa6c6697ce6 100644
--- a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -109,7 +109,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index 7f87264b45e..bd66bd2bbdc 100644
--- a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -40,7 +40,7 @@ public class FileSchemaTestClass {
   private File file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<File> files;
+  private List<File> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/NullableClass.java b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/NullableClass.java
index a89aab53e8f..6e50e2cb5ef 100644
--- a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/NullableClass.java
+++ b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/NullableClass.java
@@ -83,7 +83,7 @@ public class NullableClass extends HashMap<String, Object> {
   private JsonNullable<List<Object>> arrayAndItemsNullableProp = JsonNullable.<List<Object>>undefined();
 
   public static final String JSON_PROPERTY_ARRAY_ITEMS_NULLABLE = "array_items_nullable";
-  private List<Object> arrayItemsNullable;
+  private List<Object> arrayItemsNullable = new ArrayList<>();
 
   public static final String JSON_PROPERTY_OBJECT_NULLABLE_PROP = "object_nullable_prop";
   private JsonNullable<Map<String, Object>> objectNullableProp = JsonNullable.<Map<String, Object>>undefined();
diff --git a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
index d4148876d5d..9b6ed0f5370 100644
--- a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
+++ b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
@@ -49,7 +49,7 @@ public class ObjectWithDeprecatedFields {
   private DeprecatedObject deprecatedRef;
 
   public static final String JSON_PROPERTY_BARS = "bars";
-  private List<String> bars;
+  private List<String> bars = new ArrayList<>();
 
   public ObjectWithDeprecatedFields() {
   }
diff --git a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/Pet.java
index eb953ef03da..aa7e5813de5 100644
--- a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/Pet.java
@@ -57,7 +57,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index fe288f05fd3..0ea3273e6d0 100644
--- a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 93563735c8e..8ec937d94e4 100644
--- a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/ArrayTest.java
index 085f248e13c..8e539861d23 100644
--- a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -38,13 +38,13 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/EnumArrays.java
index f709cd80b8e..905d8f49f49 100644
--- a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -109,7 +109,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index 94b9aa8c47b..ddff4505b58 100644
--- a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -40,7 +40,7 @@ public class FileSchemaTestClass {
   private ModelFile _file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/Pet.java
index 15b15e7fb77..aa4b9b43ff5 100644
--- a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/Pet.java
@@ -57,7 +57,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/XmlItem.java b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/XmlItem.java
index 98a5a9978b4..0e34303e5ec 100644
--- a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/XmlItem.java
+++ b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/model/XmlItem.java
@@ -76,7 +76,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   public static final String JSON_PROPERTY_WRAPPED_ARRAY = "wrapped_array";
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_STRING = "name_string";
   private String nameString;
@@ -91,10 +91,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   public static final String JSON_PROPERTY_NAME_ARRAY = "name_array";
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_WRAPPED_ARRAY = "name_wrapped_array";
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_STRING = "prefix_string";
   private String prefixString;
@@ -109,10 +109,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   public static final String JSON_PROPERTY_PREFIX_ARRAY = "prefix_array";
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_STRING = "namespace_string";
   private String namespaceString;
@@ -127,10 +127,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   public static final String JSON_PROPERTY_NAMESPACE_ARRAY = "namespace_array";
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_STRING = "prefix_ns_string";
   private String prefixNsString;
@@ -145,10 +145,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   public static final String JSON_PROPERTY_PREFIX_NS_ARRAY = "prefix_ns_array";
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem() {
   }
diff --git a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index efff0de5d11..15863dc3389 100644
--- a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -38,7 +38,7 @@ import org.openapitools.client.JSON;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() { 
   }
diff --git a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index a4c81969a86..a06f9bb8876 100644
--- a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -38,7 +38,7 @@ import org.openapitools.client.JSON;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() { 
   }
diff --git a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/ArrayTest.java
index 3c45dfb980b..2f8ed7a52b0 100644
--- a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -40,13 +40,13 @@ import org.openapitools.client.JSON;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() { 
   }
diff --git a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/EnumArrays.java
index f6ebb1453b3..faa32a79a58 100644
--- a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -111,7 +111,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() { 
   }
diff --git a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index a5a2fd172b1..2c1bb74d31f 100644
--- a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -42,7 +42,7 @@ public class FileSchemaTestClass {
   private ModelFile _file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() { 
   }
diff --git a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/Pet.java
index 14959bfb6f4..9fe99a6ee96 100644
--- a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/Pet.java
@@ -59,7 +59,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/XmlItem.java b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/XmlItem.java
index 60756ea0c68..6cb354e254b 100644
--- a/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/XmlItem.java
+++ b/samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/model/XmlItem.java
@@ -78,7 +78,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   public static final String JSON_PROPERTY_WRAPPED_ARRAY = "wrapped_array";
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_STRING = "name_string";
   private String nameString;
@@ -93,10 +93,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   public static final String JSON_PROPERTY_NAME_ARRAY = "name_array";
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_WRAPPED_ARRAY = "name_wrapped_array";
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_STRING = "prefix_string";
   private String prefixString;
@@ -111,10 +111,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   public static final String JSON_PROPERTY_PREFIX_ARRAY = "prefix_array";
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_STRING = "namespace_string";
   private String namespaceString;
@@ -129,10 +129,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   public static final String JSON_PROPERTY_NAMESPACE_ARRAY = "namespace_array";
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_STRING = "prefix_ns_string";
   private String prefixNsString;
@@ -147,10 +147,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   public static final String JSON_PROPERTY_PREFIX_NS_ARRAY = "prefix_ns_array";
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem() { 
   }
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index efff0de5d11..15863dc3389 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -38,7 +38,7 @@ import org.openapitools.client.JSON;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() { 
   }
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index a4c81969a86..a06f9bb8876 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -38,7 +38,7 @@ import org.openapitools.client.JSON;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() { 
   }
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayTest.java
index 3c45dfb980b..2f8ed7a52b0 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -40,13 +40,13 @@ import org.openapitools.client.JSON;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() { 
   }
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/EnumArrays.java
index f6ebb1453b3..faa32a79a58 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -111,7 +111,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() { 
   }
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index a5a2fd172b1..2c1bb74d31f 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -42,7 +42,7 @@ public class FileSchemaTestClass {
   private ModelFile _file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() { 
   }
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/Pet.java
index 14959bfb6f4..9fe99a6ee96 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/Pet.java
@@ -59,7 +59,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/XmlItem.java b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/XmlItem.java
index 60756ea0c68..6cb354e254b 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/XmlItem.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/XmlItem.java
@@ -78,7 +78,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   public static final String JSON_PROPERTY_WRAPPED_ARRAY = "wrapped_array";
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_STRING = "name_string";
   private String nameString;
@@ -93,10 +93,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   public static final String JSON_PROPERTY_NAME_ARRAY = "name_array";
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_WRAPPED_ARRAY = "name_wrapped_array";
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_STRING = "prefix_string";
   private String prefixString;
@@ -111,10 +111,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   public static final String JSON_PROPERTY_PREFIX_ARRAY = "prefix_array";
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_STRING = "namespace_string";
   private String namespaceString;
@@ -129,10 +129,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   public static final String JSON_PROPERTY_NAMESPACE_ARRAY = "namespace_array";
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_STRING = "prefix_ns_string";
   private String prefixNsString;
@@ -147,10 +147,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   public static final String JSON_PROPERTY_PREFIX_NS_ARRAY = "prefix_ns_array";
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem() { 
   }
diff --git a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index ee57aa479cb..d098d5c109c 100644
--- a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -38,7 +38,7 @@ import org.openapitools.client.JSON;
 @jakarta.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() { 
   }
diff --git a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 22bafa5d850..5a5e95ae170 100644
--- a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -38,7 +38,7 @@ import org.openapitools.client.JSON;
 @jakarta.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() { 
   }
diff --git a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ArrayTest.java
index 184bac912c1..4906f59b726 100644
--- a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -40,13 +40,13 @@ import org.openapitools.client.JSON;
 @jakarta.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() { 
   }
diff --git a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/Drawing.java b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/Drawing.java
index 38a9d39a47c..8d80c87ae7b 100644
--- a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/Drawing.java
+++ b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/Drawing.java
@@ -61,7 +61,7 @@ public class Drawing {
   private JsonNullable<NullableShape> nullableShape = JsonNullable.<NullableShape>undefined();
 
   public static final String JSON_PROPERTY_SHAPES = "shapes";
-  private List<Shape> shapes;
+  private List<Shape> shapes = new ArrayList<>();
 
   public Drawing() { 
   }
diff --git a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/EnumArrays.java
index 13fe3462a2b..0633895619c 100644
--- a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -111,7 +111,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() { 
   }
diff --git a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index fd2bb1c706d..b2dbe47f70c 100644
--- a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -42,7 +42,7 @@ public class FileSchemaTestClass {
   private ModelFile _file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() { 
   }
diff --git a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/NullableClass.java b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/NullableClass.java
index 204310d7aab..0c0250262b9 100644
--- a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/NullableClass.java
+++ b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/NullableClass.java
@@ -85,7 +85,7 @@ public class NullableClass {
   private JsonNullable<List<Object>> arrayAndItemsNullableProp = JsonNullable.<List<Object>>undefined();
 
   public static final String JSON_PROPERTY_ARRAY_ITEMS_NULLABLE = "array_items_nullable";
-  private List<Object> arrayItemsNullable;
+  private List<Object> arrayItemsNullable = new ArrayList<>();
 
   public static final String JSON_PROPERTY_OBJECT_NULLABLE_PROP = "object_nullable_prop";
   private JsonNullable<Map<String, Object>> objectNullableProp = JsonNullable.<Map<String, Object>>undefined();
diff --git a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
index a2e92db479e..a29f9b9bdc5 100644
--- a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
+++ b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
@@ -54,7 +54,7 @@ public class ObjectWithDeprecatedFields {
 
   public static final String JSON_PROPERTY_BARS = "bars";
   @Deprecated
-  private List<String> bars;
+  private List<String> bars = new ArrayList<>();
 
   public ObjectWithDeprecatedFields() { 
   }
diff --git a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/Pet.java
index 9510806b32c..6fb9a54e91f 100644
--- a/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/model/Pet.java
@@ -56,7 +56,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index 469c0419e60..8e64ff15a0f 100644
--- a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -40,7 +40,7 @@ import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() { 
   }
diff --git a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index a5c8b50e386..7b1a2f29341 100644
--- a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -40,7 +40,7 @@ import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() { 
   }
diff --git a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ArrayTest.java
index 5f1581ac09b..64bd8fca183 100644
--- a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -42,13 +42,13 @@ import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() { 
   }
diff --git a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Drawing.java b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Drawing.java
index dde2444cf5b..969325b5545 100644
--- a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Drawing.java
+++ b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Drawing.java
@@ -65,7 +65,7 @@ public class Drawing extends HashMap<String, Fruit> {
   private JsonNullable<NullableShape> nullableShape = JsonNullable.<NullableShape>undefined();
 
   public static final String JSON_PROPERTY_SHAPES = "shapes";
-  private List<Shape> shapes;
+  private List<Shape> shapes = new ArrayList<>();
 
   public Drawing() { 
   }
diff --git a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/EnumArrays.java
index 871e0b69f25..fe3288d87ae 100644
--- a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -113,7 +113,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() { 
   }
diff --git a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index e4e8dc2c859..6a3d6e8ee74 100644
--- a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -44,7 +44,7 @@ public class FileSchemaTestClass {
   private ModelFile _file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() { 
   }
diff --git a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/NullableClass.java b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/NullableClass.java
index c284ab62576..abf2c83d2de 100644
--- a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/NullableClass.java
+++ b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/NullableClass.java
@@ -87,7 +87,7 @@ public class NullableClass extends HashMap<String, Object> {
   private JsonNullable<List<Object>> arrayAndItemsNullableProp = JsonNullable.<List<Object>>undefined();
 
   public static final String JSON_PROPERTY_ARRAY_ITEMS_NULLABLE = "array_items_nullable";
-  private List<Object> arrayItemsNullable;
+  private List<Object> arrayItemsNullable = new ArrayList<>();
 
   public static final String JSON_PROPERTY_OBJECT_NULLABLE_PROP = "object_nullable_prop";
   private JsonNullable<Map<String, Object>> objectNullableProp = JsonNullable.<Map<String, Object>>undefined();
diff --git a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
index 16fe649daf5..f98f8641eaf 100644
--- a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
+++ b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
@@ -53,7 +53,7 @@ public class ObjectWithDeprecatedFields {
   private DeprecatedObject deprecatedRef;
 
   public static final String JSON_PROPERTY_BARS = "bars";
-  private List<String> bars;
+  private List<String> bars = new ArrayList<>();
 
   public ObjectWithDeprecatedFields() { 
   }
diff --git a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Pet.java
index 5aa1a4f0732..4db13f7af50 100644
--- a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Pet.java
@@ -58,7 +58,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/native-jakarta/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/native-jakarta/src/main/java/org/openapitools/client/model/Pet.java
index 082ae002630..197f81a7511 100644
--- a/samples/client/petstore/java/native-jakarta/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/native-jakarta/src/main/java/org/openapitools/client/model/Pet.java
@@ -58,7 +58,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index 469c0419e60..8e64ff15a0f 100644
--- a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -40,7 +40,7 @@ import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() { 
   }
diff --git a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index a5c8b50e386..7b1a2f29341 100644
--- a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -40,7 +40,7 @@ import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() { 
   }
diff --git a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ArrayTest.java
index 5f1581ac09b..64bd8fca183 100644
--- a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -42,13 +42,13 @@ import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() { 
   }
diff --git a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Drawing.java b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Drawing.java
index dde2444cf5b..969325b5545 100644
--- a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Drawing.java
+++ b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Drawing.java
@@ -65,7 +65,7 @@ public class Drawing extends HashMap<String, Fruit> {
   private JsonNullable<NullableShape> nullableShape = JsonNullable.<NullableShape>undefined();
 
   public static final String JSON_PROPERTY_SHAPES = "shapes";
-  private List<Shape> shapes;
+  private List<Shape> shapes = new ArrayList<>();
 
   public Drawing() { 
   }
diff --git a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/EnumArrays.java
index 871e0b69f25..fe3288d87ae 100644
--- a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -113,7 +113,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() { 
   }
diff --git a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index e4e8dc2c859..6a3d6e8ee74 100644
--- a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -44,7 +44,7 @@ public class FileSchemaTestClass {
   private ModelFile _file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() { 
   }
diff --git a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/NullableClass.java b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/NullableClass.java
index c284ab62576..abf2c83d2de 100644
--- a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/NullableClass.java
+++ b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/NullableClass.java
@@ -87,7 +87,7 @@ public class NullableClass extends HashMap<String, Object> {
   private JsonNullable<List<Object>> arrayAndItemsNullableProp = JsonNullable.<List<Object>>undefined();
 
   public static final String JSON_PROPERTY_ARRAY_ITEMS_NULLABLE = "array_items_nullable";
-  private List<Object> arrayItemsNullable;
+  private List<Object> arrayItemsNullable = new ArrayList<>();
 
   public static final String JSON_PROPERTY_OBJECT_NULLABLE_PROP = "object_nullable_prop";
   private JsonNullable<Map<String, Object>> objectNullableProp = JsonNullable.<Map<String, Object>>undefined();
diff --git a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
index 16fe649daf5..f98f8641eaf 100644
--- a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
+++ b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
@@ -53,7 +53,7 @@ public class ObjectWithDeprecatedFields {
   private DeprecatedObject deprecatedRef;
 
   public static final String JSON_PROPERTY_BARS = "bars";
-  private List<String> bars;
+  private List<String> bars = new ArrayList<>();
 
   public ObjectWithDeprecatedFields() { 
   }
diff --git a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Pet.java
index 5aa1a4f0732..4db13f7af50 100644
--- a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Pet.java
@@ -58,7 +58,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/AnyTypeTest.java b/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/AnyTypeTest.java
index ccb0ebdd03a..abb82b6bae9 100644
--- a/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/AnyTypeTest.java
+++ b/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/AnyTypeTest.java
@@ -60,11 +60,11 @@ public class AnyTypeTest {
 
   public static final String SERIALIZED_NAME_ARRAY_PROP = "array_prop";
   @SerializedName(SERIALIZED_NAME_ARRAY_PROP)
-  private List<String> arrayProp;
+  private List<String> arrayProp = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_REF_ARRAY_PREFIX_ITEMS = "ref_array_prefix_items";
   @SerializedName(SERIALIZED_NAME_REF_ARRAY_PREFIX_ITEMS)
-  private List<String> refArrayPrefixItems;
+  private List<String> refArrayPrefixItems = new ArrayList<>();
 
   public AnyTypeTest() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/Pet.java
index 018cf45179c..d84f4cd4400 100644
--- a/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/model/Pet.java
@@ -73,7 +73,7 @@ public class Pet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/okhttp-gson-awsv4signature/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/okhttp-gson-awsv4signature/src/main/java/org/openapitools/client/model/Pet.java
index 018cf45179c..d84f4cd4400 100644
--- a/samples/client/petstore/java/okhttp-gson-awsv4signature/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/okhttp-gson-awsv4signature/src/main/java/org/openapitools/client/model/Pet.java
@@ -73,7 +73,7 @@ public class Pet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index 6efd1c01ce1..33674370dd2 100644
--- a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -56,7 +56,7 @@ import org.openapitools.client.JSON;
 public class ArrayOfArrayOfNumberOnly {
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_NUMBER)
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index d1b40393b7b..cad0e1a432b 100644
--- a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -56,7 +56,7 @@ import org.openapitools.client.JSON;
 public class ArrayOfNumberOnly {
   public static final String SERIALIZED_NAME_ARRAY_NUMBER = "ArrayNumber";
   @SerializedName(SERIALIZED_NAME_ARRAY_NUMBER)
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/ArrayTest.java
index 331a44e603b..0f39fa95cb8 100644
--- a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -56,15 +56,15 @@ import org.openapitools.client.JSON;
 public class ArrayTest {
   public static final String SERIALIZED_NAME_ARRAY_OF_STRING = "array_of_string";
   @SerializedName(SERIALIZED_NAME_ARRAY_OF_STRING)
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_OF_INTEGER)
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_OF_MODEL)
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/EnumArrays.java
index dd38bbbf1e1..569f80c4ae4 100644
--- a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -163,7 +163,7 @@ public class EnumArrays {
 
   public static final String SERIALIZED_NAME_ARRAY_ENUM = "array_enum";
   @SerializedName(SERIALIZED_NAME_ARRAY_ENUM)
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index 2ecc75b87a9..ff1c556b876 100644
--- a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -60,7 +60,7 @@ public class FileSchemaTestClass {
 
   public static final String SERIALIZED_NAME_FILES = "files";
   @SerializedName(SERIALIZED_NAME_FILES)
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/Pet.java
index ee1eeca2d44..4540a26bd7a 100644
--- a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/Pet.java
@@ -75,7 +75,7 @@ public class Pet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/XmlItem.java b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/XmlItem.java
index 6aba37401a2..1333ca76a0a 100644
--- a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/XmlItem.java
+++ b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/XmlItem.java
@@ -72,7 +72,7 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_WRAPPED_ARRAY = "wrapped_array";
   @SerializedName(SERIALIZED_NAME_WRAPPED_ARRAY)
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAME_STRING = "name_string";
   @SerializedName(SERIALIZED_NAME_NAME_STRING)
@@ -92,11 +92,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_NAME_ARRAY = "name_array";
   @SerializedName(SERIALIZED_NAME_NAME_ARRAY)
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAME_WRAPPED_ARRAY = "name_wrapped_array";
   @SerializedName(SERIALIZED_NAME_NAME_WRAPPED_ARRAY)
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_STRING = "prefix_string";
   @SerializedName(SERIALIZED_NAME_PREFIX_STRING)
@@ -116,11 +116,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_PREFIX_ARRAY = "prefix_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_ARRAY)
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_WRAPPED_ARRAY)
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAMESPACE_STRING = "namespace_string";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_STRING)
@@ -140,11 +140,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_NAMESPACE_ARRAY = "namespace_array";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_ARRAY)
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_WRAPPED_ARRAY)
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_NS_STRING = "prefix_ns_string";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_STRING)
@@ -164,11 +164,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_PREFIX_NS_ARRAY = "prefix_ns_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_ARRAY)
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_WRAPPED_ARRAY)
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson-group-parameter/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/okhttp-gson-group-parameter/src/main/java/org/openapitools/client/model/Pet.java
index 018cf45179c..d84f4cd4400 100644
--- a/samples/client/petstore/java/okhttp-gson-group-parameter/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/okhttp-gson-group-parameter/src/main/java/org/openapitools/client/model/Pet.java
@@ -73,7 +73,7 @@ public class Pet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/okhttp-gson-nullable-required/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/okhttp-gson-nullable-required/src/main/java/org/openapitools/client/model/Pet.java
index 018cf45179c..d84f4cd4400 100644
--- a/samples/client/petstore/java/okhttp-gson-nullable-required/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/okhttp-gson-nullable-required/src/main/java/org/openapitools/client/model/Pet.java
@@ -73,7 +73,7 @@ public class Pet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/okhttp-gson-nullable-required/src/main/java/org/openapitools/client/model/PetWithRequiredNullableCases2.java b/samples/client/petstore/java/okhttp-gson-nullable-required/src/main/java/org/openapitools/client/model/PetWithRequiredNullableCases2.java
index f069fbd56ee..d4af44a9fa7 100644
--- a/samples/client/petstore/java/okhttp-gson-nullable-required/src/main/java/org/openapitools/client/model/PetWithRequiredNullableCases2.java
+++ b/samples/client/petstore/java/okhttp-gson-nullable-required/src/main/java/org/openapitools/client/model/PetWithRequiredNullableCases2.java
@@ -73,7 +73,7 @@ public class PetWithRequiredNullableCases2 {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index 77a08ee47b0..2dd0fac4f7a 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -58,7 +58,7 @@ import org.openapitools.client.JSON;
 public class ArrayOfArrayOfNumberOnly implements Parcelable {
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_NUMBER)
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index d0823c0499c..15b061615da 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -58,7 +58,7 @@ import org.openapitools.client.JSON;
 public class ArrayOfNumberOnly implements Parcelable {
   public static final String SERIALIZED_NAME_ARRAY_NUMBER = "ArrayNumber";
   @SerializedName(SERIALIZED_NAME_ARRAY_NUMBER)
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/ArrayTest.java
index f5c1325b7e7..e26bbfe69d2 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -58,15 +58,15 @@ import org.openapitools.client.JSON;
 public class ArrayTest implements Parcelable {
   public static final String SERIALIZED_NAME_ARRAY_OF_STRING = "array_of_string";
   @SerializedName(SERIALIZED_NAME_ARRAY_OF_STRING)
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_OF_INTEGER)
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_OF_MODEL)
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/EnumArrays.java
index 45b6fdddeda..f7d71fd5965 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -165,7 +165,7 @@ public class EnumArrays implements Parcelable {
 
   public static final String SERIALIZED_NAME_ARRAY_ENUM = "array_enum";
   @SerializedName(SERIALIZED_NAME_ARRAY_ENUM)
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index 80fc055b9d0..04ec0359a3d 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -62,7 +62,7 @@ public class FileSchemaTestClass implements Parcelable {
 
   public static final String SERIALIZED_NAME_FILES = "files";
   @SerializedName(SERIALIZED_NAME_FILES)
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/Pet.java
index fb1066a4872..f89d551dbff 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/Pet.java
@@ -77,7 +77,7 @@ public class Pet implements Parcelable {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/XmlItem.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/XmlItem.java
index 7a9cc1ae938..1249602d134 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/XmlItem.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/XmlItem.java
@@ -74,7 +74,7 @@ public class XmlItem implements Parcelable {
 
   public static final String SERIALIZED_NAME_WRAPPED_ARRAY = "wrapped_array";
   @SerializedName(SERIALIZED_NAME_WRAPPED_ARRAY)
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAME_STRING = "name_string";
   @SerializedName(SERIALIZED_NAME_NAME_STRING)
@@ -94,11 +94,11 @@ public class XmlItem implements Parcelable {
 
   public static final String SERIALIZED_NAME_NAME_ARRAY = "name_array";
   @SerializedName(SERIALIZED_NAME_NAME_ARRAY)
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAME_WRAPPED_ARRAY = "name_wrapped_array";
   @SerializedName(SERIALIZED_NAME_NAME_WRAPPED_ARRAY)
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_STRING = "prefix_string";
   @SerializedName(SERIALIZED_NAME_PREFIX_STRING)
@@ -118,11 +118,11 @@ public class XmlItem implements Parcelable {
 
   public static final String SERIALIZED_NAME_PREFIX_ARRAY = "prefix_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_ARRAY)
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_WRAPPED_ARRAY)
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAMESPACE_STRING = "namespace_string";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_STRING)
@@ -142,11 +142,11 @@ public class XmlItem implements Parcelable {
 
   public static final String SERIALIZED_NAME_NAMESPACE_ARRAY = "namespace_array";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_ARRAY)
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_WRAPPED_ARRAY)
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_NS_STRING = "prefix_ns_string";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_STRING)
@@ -166,11 +166,11 @@ public class XmlItem implements Parcelable {
 
   public static final String SERIALIZED_NAME_PREFIX_NS_ARRAY = "prefix_ns_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_ARRAY)
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_WRAPPED_ARRAY)
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson-swagger1/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/okhttp-gson-swagger1/src/main/java/org/openapitools/client/model/Pet.java
index ecc2d598781..03ca4a1fe93 100644
--- a/samples/client/petstore/java/okhttp-gson-swagger1/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/okhttp-gson-swagger1/src/main/java/org/openapitools/client/model/Pet.java
@@ -76,7 +76,7 @@ public class Pet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/okhttp-gson-swagger2/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/okhttp-gson-swagger2/src/main/java/org/openapitools/client/model/Pet.java
index f1ef9a7b5a1..138d53b4579 100644
--- a/samples/client/petstore/java/okhttp-gson-swagger2/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/okhttp-gson-swagger2/src/main/java/org/openapitools/client/model/Pet.java
@@ -75,7 +75,7 @@ public class Pet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayDefault.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayDefault.java
index bad7ce1cb01..780c3374c18 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayDefault.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayDefault.java
@@ -59,7 +59,7 @@ public class ArrayDefault {
 
   public static final String SERIALIZED_NAME_WITHOUT_DEFAULT = "WithoutDefault";
   @SerializedName(SERIALIZED_NAME_WITHOUT_DEFAULT)
-  private List<String> withoutDefault;
+  private List<String> withoutDefault = new ArrayList<>();
 
   public ArrayDefault() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index 25b9d4f32b6..f84ff18b454 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -56,7 +56,7 @@ import org.openapitools.client.JSON;
 public class ArrayOfArrayOfNumberOnly {
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_NUMBER)
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayOfInlineAllOf.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayOfInlineAllOf.java
index 872b119941e..3ed5fc3c1e5 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayOfInlineAllOf.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayOfInlineAllOf.java
@@ -64,7 +64,7 @@ public class ArrayOfInlineAllOf {
 
   public static final String SERIALIZED_NAME_ARRAY_ALLOF_DOG_PROPERTY = "array_allof_dog_property";
   @SerializedName(SERIALIZED_NAME_ARRAY_ALLOF_DOG_PROPERTY)
-  private List<ArrayOfInlineAllOfArrayAllofDogPropertyInner> arrayAllofDogProperty;
+  private List<ArrayOfInlineAllOfArrayAllofDogPropertyInner> arrayAllofDogProperty = new ArrayList<>();
 
   public ArrayOfInlineAllOf() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index f3bf58227dc..c27568aae20 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -56,7 +56,7 @@ import org.openapitools.client.JSON;
 public class ArrayOfNumberOnly {
   public static final String SERIALIZED_NAME_ARRAY_NUMBER = "ArrayNumber";
   @SerializedName(SERIALIZED_NAME_ARRAY_NUMBER)
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayTest.java
index 7f815e7f934..a49b4598b6c 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -56,15 +56,15 @@ import org.openapitools.client.JSON;
 public class ArrayTest {
   public static final String SERIALIZED_NAME_ARRAY_OF_STRING = "array_of_string";
   @SerializedName(SERIALIZED_NAME_ARRAY_OF_STRING)
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_OF_INTEGER)
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_OF_MODEL)
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/Drawing.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/Drawing.java
index e9573171bc3..d6dac39f8d1 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/Drawing.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/Drawing.java
@@ -72,7 +72,7 @@ public class Drawing {
 
   public static final String SERIALIZED_NAME_SHAPES = "shapes";
   @SerializedName(SERIALIZED_NAME_SHAPES)
-  private List<Shape> shapes;
+  private List<Shape> shapes = new ArrayList<>();
 
   public Drawing() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/EnumArrays.java
index 4daa8f31434..53f4c7b1107 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -163,7 +163,7 @@ public class EnumArrays {
 
   public static final String SERIALIZED_NAME_ARRAY_ENUM = "array_enum";
   @SerializedName(SERIALIZED_NAME_ARRAY_ENUM)
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index 3af995cc7b0..4a8d5b4d317 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -60,7 +60,7 @@ public class FileSchemaTestClass {
 
   public static final String SERIALIZED_NAME_FILES = "files";
   @SerializedName(SERIALIZED_NAME_FILES)
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/NewPet.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/NewPet.java
index 7166f45fc02..d1bd00ff00b 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/NewPet.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/NewPet.java
@@ -78,7 +78,7 @@ public class NewPet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/NullableClass.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/NullableClass.java
index 0d5e79d9ec7..8fe3e9b7507 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/NullableClass.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/NullableClass.java
@@ -93,7 +93,7 @@ public class NullableClass {
 
   public static final String SERIALIZED_NAME_ARRAY_ITEMS_NULLABLE = "array_items_nullable";
   @SerializedName(SERIALIZED_NAME_ARRAY_ITEMS_NULLABLE)
-  private List<Object> arrayItemsNullable;
+  private List<Object> arrayItemsNullable = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_OBJECT_NULLABLE_PROP = "object_nullable_prop";
   @SerializedName(SERIALIZED_NAME_OBJECT_NULLABLE_PROP)
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
index 17072735f46..7d2e6cd60ec 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
@@ -72,7 +72,7 @@ public class ObjectWithDeprecatedFields {
   public static final String SERIALIZED_NAME_BARS = "bars";
   @Deprecated
   @SerializedName(SERIALIZED_NAME_BARS)
-  private List<String> bars;
+  private List<String> bars = new ArrayList<>();
 
   public ObjectWithDeprecatedFields() {
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/Pet.java
index 1c62646bd9f..e285620bb34 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/Pet.java
@@ -73,7 +73,7 @@ public class Pet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/PetUsingAllOf.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/PetUsingAllOf.java
index 4bef75ff1a4..87929642590 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/PetUsingAllOf.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/PetUsingAllOf.java
@@ -73,7 +73,7 @@ public class PetUsingAllOf {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index d146bd37c86..bdcef50d874 100644
--- a/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -39,7 +39,7 @@ import org.hibernate.validator.constraints.*;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 1967108db6e..67df71a4dec 100644
--- a/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -39,7 +39,7 @@ import org.hibernate.validator.constraints.*;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/ArrayTest.java
index 9cd62d1ea57..23766602072 100644
--- a/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -41,13 +41,13 @@ import org.hibernate.validator.constraints.*;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/EnumArrays.java
index 5a84534acec..8fa284cd1c5 100644
--- a/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -112,7 +112,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index c78326f540f..d6df3224e06 100644
--- a/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -43,7 +43,7 @@ public class FileSchemaTestClass {
   private ModelFile _file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<@Valid ModelFile> files;
+  private List<@Valid ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/Pet.java
index 6ac3a121e5c..3a1d97800ff 100644
--- a/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/Pet.java
@@ -60,7 +60,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/XmlItem.java b/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/XmlItem.java
index 33d3d8dc56b..d83ecbd8b35 100644
--- a/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/XmlItem.java
+++ b/samples/client/petstore/java/rest-assured-jackson/src/main/java/org/openapitools/client/model/XmlItem.java
@@ -79,7 +79,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   public static final String JSON_PROPERTY_WRAPPED_ARRAY = "wrapped_array";
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_STRING = "name_string";
   private String nameString;
@@ -94,10 +94,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   public static final String JSON_PROPERTY_NAME_ARRAY = "name_array";
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_WRAPPED_ARRAY = "name_wrapped_array";
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_STRING = "prefix_string";
   private String prefixString;
@@ -112,10 +112,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   public static final String JSON_PROPERTY_PREFIX_ARRAY = "prefix_array";
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_STRING = "namespace_string";
   private String namespaceString;
@@ -130,10 +130,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   public static final String JSON_PROPERTY_NAMESPACE_ARRAY = "namespace_array";
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_STRING = "prefix_ns_string";
   private String prefixNsString;
@@ -148,10 +148,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   public static final String JSON_PROPERTY_PREFIX_NS_ARRAY = "prefix_ns_array";
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem() {
   }
diff --git a/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index 9de61914135..e90bbf254c8 100644
--- a/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import org.hibernate.validator.constraints.*;
 public class ArrayOfArrayOfNumberOnly {
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_NUMBER)
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 507a5cfd6a8..aa016ab88a4 100644
--- a/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import org.hibernate.validator.constraints.*;
 public class ArrayOfNumberOnly {
   public static final String SERIALIZED_NAME_ARRAY_NUMBER = "ArrayNumber";
   @SerializedName(SERIALIZED_NAME_ARRAY_NUMBER)
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/ArrayTest.java
index 665dc39b320..e9c4e65fd9e 100644
--- a/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -36,15 +36,15 @@ import org.hibernate.validator.constraints.*;
 public class ArrayTest {
   public static final String SERIALIZED_NAME_ARRAY_OF_STRING = "array_of_string";
   @SerializedName(SERIALIZED_NAME_ARRAY_OF_STRING)
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_OF_INTEGER)
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_OF_MODEL)
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/EnumArrays.java
index ae1c8664e65..8d3e0088fe2 100644
--- a/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -133,7 +133,7 @@ public class EnumArrays {
 
   public static final String SERIALIZED_NAME_ARRAY_ENUM = "array_enum";
   @SerializedName(SERIALIZED_NAME_ARRAY_ENUM)
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index 154d967daaf..5eb3ab845b1 100644
--- a/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -40,7 +40,7 @@ public class FileSchemaTestClass {
 
   public static final String SERIALIZED_NAME_FILES = "files";
   @SerializedName(SERIALIZED_NAME_FILES)
-  private List<@Valid ModelFile> files;
+  private List<@Valid ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/Pet.java
index 9ae7e9a397a..63c242266c2 100644
--- a/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/Pet.java
@@ -55,7 +55,7 @@ public class Pet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/XmlItem.java b/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/XmlItem.java
index 155b81e206d..14e5bd20c8a 100644
--- a/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/XmlItem.java
+++ b/samples/client/petstore/java/rest-assured/src/main/java/org/openapitools/client/model/XmlItem.java
@@ -52,7 +52,7 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_WRAPPED_ARRAY = "wrapped_array";
   @SerializedName(SERIALIZED_NAME_WRAPPED_ARRAY)
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAME_STRING = "name_string";
   @SerializedName(SERIALIZED_NAME_NAME_STRING)
@@ -72,11 +72,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_NAME_ARRAY = "name_array";
   @SerializedName(SERIALIZED_NAME_NAME_ARRAY)
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAME_WRAPPED_ARRAY = "name_wrapped_array";
   @SerializedName(SERIALIZED_NAME_NAME_WRAPPED_ARRAY)
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_STRING = "prefix_string";
   @SerializedName(SERIALIZED_NAME_PREFIX_STRING)
@@ -96,11 +96,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_PREFIX_ARRAY = "prefix_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_ARRAY)
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_WRAPPED_ARRAY)
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAMESPACE_STRING = "namespace_string";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_STRING)
@@ -120,11 +120,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_NAMESPACE_ARRAY = "namespace_array";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_ARRAY)
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_WRAPPED_ARRAY)
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_NS_STRING = "prefix_ns_string";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_STRING)
@@ -144,11 +144,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_PREFIX_NS_ARRAY = "prefix_ns_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_ARRAY)
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_WRAPPED_ARRAY)
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem() {
   }
diff --git a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index fe288f05fd3..0ea3273e6d0 100644
--- a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 93563735c8e..8ec937d94e4 100644
--- a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ArrayTest.java
index 085f248e13c..8e539861d23 100644
--- a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -38,13 +38,13 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/EnumArrays.java
index f709cd80b8e..905d8f49f49 100644
--- a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -109,7 +109,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index 94b9aa8c47b..ddff4505b58 100644
--- a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -40,7 +40,7 @@ public class FileSchemaTestClass {
   private ModelFile _file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/NullableClass.java b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/NullableClass.java
index 59eba1ade73..58c4c2d1bdc 100644
--- a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/NullableClass.java
+++ b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/NullableClass.java
@@ -79,7 +79,7 @@ public class NullableClass extends HashMap<String, Object> {
   private JsonNullable<List<Object>> arrayAndItemsNullableProp = JsonNullable.<List<Object>>undefined();
 
   public static final String JSON_PROPERTY_ARRAY_ITEMS_NULLABLE = "array_items_nullable";
-  private List<Object> arrayItemsNullable;
+  private List<Object> arrayItemsNullable = new ArrayList<>();
 
   public static final String JSON_PROPERTY_OBJECT_NULLABLE_PROP = "object_nullable_prop";
   private JsonNullable<Map<String, Object>> objectNullableProp = JsonNullable.<Map<String, Object>>undefined();
diff --git a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
index 2dc51d40f65..6699a31ae15 100644
--- a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
+++ b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
@@ -49,7 +49,7 @@ public class ObjectWithDeprecatedFields {
   private DeprecatedObject deprecatedRef;
 
   public static final String JSON_PROPERTY_BARS = "bars";
-  private List<String> bars;
+  private List<String> bars = new ArrayList<>();
 
   public ObjectWithDeprecatedFields() {
   }
diff --git a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/Pet.java
index 15b15e7fb77..aa4b9b43ff5 100644
--- a/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/resteasy/src/main/java/org/openapitools/client/model/Pet.java
@@ -57,7 +57,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/resttemplate-jakarta/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/resttemplate-jakarta/src/main/java/org/openapitools/client/model/Pet.java
index 092b552a63b..7d73cad29f6 100644
--- a/samples/client/petstore/java/resttemplate-jakarta/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/resttemplate-jakarta/src/main/java/org/openapitools/client/model/Pet.java
@@ -54,7 +54,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/resttemplate-swagger1/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/resttemplate-swagger1/src/main/java/org/openapitools/client/model/Pet.java
index 73b6797b36d..173a736a770 100644
--- a/samples/client/petstore/java/resttemplate-swagger1/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/resttemplate-swagger1/src/main/java/org/openapitools/client/model/Pet.java
@@ -57,7 +57,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/resttemplate-swagger2/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/resttemplate-swagger2/src/main/java/org/openapitools/client/model/Pet.java
index feee610426f..5b8ed31ec21 100644
--- a/samples/client/petstore/java/resttemplate-swagger2/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/resttemplate-swagger2/src/main/java/org/openapitools/client/model/Pet.java
@@ -56,7 +56,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index 4c70df2ff63..64f7932a365 100644
--- a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -47,7 +47,7 @@ public class ArrayOfArrayOfNumberOnly {
   // items.name=arrayArrayNumber items.baseName=arrayArrayNumber items.xmlName= items.xmlNamespace=
   // items.example= items.type=List&lt;BigDecimal&gt;
   @XmlElement(name = "arrayArrayNumber")
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 0262d52ac64..1feae842c32 100644
--- a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -47,7 +47,7 @@ public class ArrayOfNumberOnly {
   // items.name=arrayNumber items.baseName=arrayNumber items.xmlName= items.xmlNamespace=
   // items.example= items.type=BigDecimal
   @XmlElement(name = "arrayNumber")
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ArrayTest.java
index 22b6510f904..b1e17c7e2d1 100644
--- a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -49,21 +49,21 @@ public class ArrayTest {
   // items.name=arrayOfString items.baseName=arrayOfString items.xmlName= items.xmlNamespace=
   // items.example= items.type=String
   @XmlElement(name = "arrayOfString")
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
   // Is a container wrapped=false
   // items.name=arrayArrayOfInteger items.baseName=arrayArrayOfInteger items.xmlName= items.xmlNamespace=
   // items.example= items.type=List&lt;Long&gt;
   @XmlElement(name = "arrayArrayOfInteger")
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
   // Is a container wrapped=false
   // items.name=arrayArrayOfModel items.baseName=arrayArrayOfModel items.xmlName= items.xmlNamespace=
   // items.example= items.type=List&lt;ReadOnlyFirst&gt;
   @XmlElement(name = "arrayArrayOfModel")
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/EnumArrays.java
index 7f818781a4d..9e9aeb0afcc 100644
--- a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -129,7 +129,7 @@ public class EnumArrays {
   // items.name=arrayEnum items.baseName=arrayEnum items.xmlName= items.xmlNamespace=
   // items.example= items.type=String
   @XmlElement(name = "arrayEnum")
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index d6613869f12..a0a6be321d6 100644
--- a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -52,7 +52,7 @@ public class FileSchemaTestClass {
   // items.name=files items.baseName=files items.xmlName= items.xmlNamespace=
   // items.example= items.type=ModelFile
   @XmlElement(name = "files")
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/NullableClass.java b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/NullableClass.java
index be0cb021342..a755b1072d5 100644
--- a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/NullableClass.java
+++ b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/NullableClass.java
@@ -105,7 +105,7 @@ public class NullableClass extends HashMap<String, Object> {
   // items.name=arrayItemsNullable items.baseName=arrayItemsNullable items.xmlName= items.xmlNamespace=
   // items.example= items.type=Object
   @XmlElement(name = "arrayItemsNullable")
-  private List<Object> arrayItemsNullable;
+  private List<Object> arrayItemsNullable = new ArrayList<>();
 
   public static final String JSON_PROPERTY_OBJECT_NULLABLE_PROP = "object_nullable_prop";
   // Is a container wrapped=false
diff --git a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
index 9f96571ed9c..c3fa7fd7f3d 100644
--- a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
+++ b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
@@ -63,7 +63,7 @@ public class ObjectWithDeprecatedFields {
   // items.name=bars items.baseName=bars items.xmlName= items.xmlNamespace=
   // items.example= items.type=String
   @XmlElement(name = "bars")
-  private List<String> bars;
+  private List<String> bars = new ArrayList<>();
 
   public ObjectWithDeprecatedFields() {
   }
diff --git a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/Pet.java
index a140c0cff0d..220fc766c32 100644
--- a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/model/Pet.java
@@ -77,7 +77,7 @@ public class Pet {
   // items.example= items.type=Tag
   @XmlElement(name = "Tag")
   @XmlElementWrapper(name = "tag")
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index 75d4e6f13f9..6e049dcf798 100644
--- a/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -38,7 +38,7 @@ import javax.validation.Valid;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 7cb82a01c51..53c2147b1ff 100644
--- a/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -38,7 +38,7 @@ import javax.validation.Valid;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/ArrayTest.java
index 7c538c1ae18..2246f98cf06 100644
--- a/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -40,13 +40,13 @@ import javax.validation.Valid;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/EnumArrays.java
index 657273e35a0..fd47809aaef 100644
--- a/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -111,7 +111,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index 075edc93285..f656e826e67 100644
--- a/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -42,7 +42,7 @@ public class FileSchemaTestClass {
   private ModelFile _file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<@Valid ModelFile> files;
+  private List<@Valid ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/Pet.java
index b992cd60509..11db4a917ca 100644
--- a/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/Pet.java
@@ -59,7 +59,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/XmlItem.java b/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/XmlItem.java
index f6145623294..1880199692e 100644
--- a/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/XmlItem.java
+++ b/samples/client/petstore/java/retrofit2-play26/src/main/java/org/openapitools/client/model/XmlItem.java
@@ -78,7 +78,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   public static final String JSON_PROPERTY_WRAPPED_ARRAY = "wrapped_array";
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_STRING = "name_string";
   private String nameString;
@@ -93,10 +93,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   public static final String JSON_PROPERTY_NAME_ARRAY = "name_array";
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_WRAPPED_ARRAY = "name_wrapped_array";
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_STRING = "prefix_string";
   private String prefixString;
@@ -111,10 +111,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   public static final String JSON_PROPERTY_PREFIX_ARRAY = "prefix_array";
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_STRING = "namespace_string";
   private String namespaceString;
@@ -129,10 +129,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   public static final String JSON_PROPERTY_NAMESPACE_ARRAY = "namespace_array";
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_STRING = "prefix_ns_string";
   private String prefixNsString;
@@ -147,10 +147,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   public static final String JSON_PROPERTY_PREFIX_NS_ARRAY = "prefix_ns_array";
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem() {
   }
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index 3f40488e7b1..baa27babe1e 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -33,7 +33,7 @@ import java.util.List;
 public class ArrayOfArrayOfNumberOnly {
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_NUMBER)
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 24eacf53013..f8adf8e89c4 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -33,7 +33,7 @@ import java.util.List;
 public class ArrayOfNumberOnly {
   public static final String SERIALIZED_NAME_ARRAY_NUMBER = "ArrayNumber";
   @SerializedName(SERIALIZED_NAME_ARRAY_NUMBER)
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/ArrayTest.java
index a6c287390c8..112ec07fe10 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -33,15 +33,15 @@ import org.openapitools.client.model.ReadOnlyFirst;
 public class ArrayTest {
   public static final String SERIALIZED_NAME_ARRAY_OF_STRING = "array_of_string";
   @SerializedName(SERIALIZED_NAME_ARRAY_OF_STRING)
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_OF_INTEGER)
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_OF_MODEL)
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/EnumArrays.java
index ca9b81defcb..f181d912391 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -130,7 +130,7 @@ public class EnumArrays {
 
   public static final String SERIALIZED_NAME_ARRAY_ENUM = "array_enum";
   @SerializedName(SERIALIZED_NAME_ARRAY_ENUM)
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index ca37946be88..72c9bd874b5 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -37,7 +37,7 @@ public class FileSchemaTestClass {
 
   public static final String SERIALIZED_NAME_FILES = "files";
   @SerializedName(SERIALIZED_NAME_FILES)
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/Pet.java
index 266d3d941ca..6dae7446a9d 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/Pet.java
@@ -52,7 +52,7 @@ public class Pet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/XmlItem.java b/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/XmlItem.java
index 97278128bd8..184f09d430d 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/XmlItem.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/org/openapitools/client/model/XmlItem.java
@@ -49,7 +49,7 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_WRAPPED_ARRAY = "wrapped_array";
   @SerializedName(SERIALIZED_NAME_WRAPPED_ARRAY)
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAME_STRING = "name_string";
   @SerializedName(SERIALIZED_NAME_NAME_STRING)
@@ -69,11 +69,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_NAME_ARRAY = "name_array";
   @SerializedName(SERIALIZED_NAME_NAME_ARRAY)
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAME_WRAPPED_ARRAY = "name_wrapped_array";
   @SerializedName(SERIALIZED_NAME_NAME_WRAPPED_ARRAY)
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_STRING = "prefix_string";
   @SerializedName(SERIALIZED_NAME_PREFIX_STRING)
@@ -93,11 +93,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_PREFIX_ARRAY = "prefix_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_ARRAY)
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_WRAPPED_ARRAY)
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAMESPACE_STRING = "namespace_string";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_STRING)
@@ -117,11 +117,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_NAMESPACE_ARRAY = "namespace_array";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_ARRAY)
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_WRAPPED_ARRAY)
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_NS_STRING = "prefix_ns_string";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_STRING)
@@ -141,11 +141,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_PREFIX_NS_ARRAY = "prefix_ns_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_ARRAY)
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_WRAPPED_ARRAY)
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem() {
   }
diff --git a/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index 3f40488e7b1..baa27babe1e 100644
--- a/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -33,7 +33,7 @@ import java.util.List;
 public class ArrayOfArrayOfNumberOnly {
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_NUMBER)
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 24eacf53013..f8adf8e89c4 100644
--- a/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -33,7 +33,7 @@ import java.util.List;
 public class ArrayOfNumberOnly {
   public static final String SERIALIZED_NAME_ARRAY_NUMBER = "ArrayNumber";
   @SerializedName(SERIALIZED_NAME_ARRAY_NUMBER)
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/ArrayTest.java
index a6c287390c8..112ec07fe10 100644
--- a/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -33,15 +33,15 @@ import org.openapitools.client.model.ReadOnlyFirst;
 public class ArrayTest {
   public static final String SERIALIZED_NAME_ARRAY_OF_STRING = "array_of_string";
   @SerializedName(SERIALIZED_NAME_ARRAY_OF_STRING)
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_OF_INTEGER)
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_OF_MODEL)
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/EnumArrays.java
index ca9b81defcb..f181d912391 100644
--- a/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -130,7 +130,7 @@ public class EnumArrays {
 
   public static final String SERIALIZED_NAME_ARRAY_ENUM = "array_enum";
   @SerializedName(SERIALIZED_NAME_ARRAY_ENUM)
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index ca37946be88..72c9bd874b5 100644
--- a/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -37,7 +37,7 @@ public class FileSchemaTestClass {
 
   public static final String SERIALIZED_NAME_FILES = "files";
   @SerializedName(SERIALIZED_NAME_FILES)
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/Pet.java
index 266d3d941ca..6dae7446a9d 100644
--- a/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/Pet.java
@@ -52,7 +52,7 @@ public class Pet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/XmlItem.java b/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/XmlItem.java
index 97278128bd8..184f09d430d 100644
--- a/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/XmlItem.java
+++ b/samples/client/petstore/java/retrofit2rx2/src/main/java/org/openapitools/client/model/XmlItem.java
@@ -49,7 +49,7 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_WRAPPED_ARRAY = "wrapped_array";
   @SerializedName(SERIALIZED_NAME_WRAPPED_ARRAY)
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAME_STRING = "name_string";
   @SerializedName(SERIALIZED_NAME_NAME_STRING)
@@ -69,11 +69,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_NAME_ARRAY = "name_array";
   @SerializedName(SERIALIZED_NAME_NAME_ARRAY)
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAME_WRAPPED_ARRAY = "name_wrapped_array";
   @SerializedName(SERIALIZED_NAME_NAME_WRAPPED_ARRAY)
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_STRING = "prefix_string";
   @SerializedName(SERIALIZED_NAME_PREFIX_STRING)
@@ -93,11 +93,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_PREFIX_ARRAY = "prefix_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_ARRAY)
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_WRAPPED_ARRAY)
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAMESPACE_STRING = "namespace_string";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_STRING)
@@ -117,11 +117,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_NAMESPACE_ARRAY = "namespace_array";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_ARRAY)
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_WRAPPED_ARRAY)
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_NS_STRING = "prefix_ns_string";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_STRING)
@@ -141,11 +141,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_PREFIX_NS_ARRAY = "prefix_ns_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_ARRAY)
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_WRAPPED_ARRAY)
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem() {
   }
diff --git a/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index 3f40488e7b1..baa27babe1e 100644
--- a/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -33,7 +33,7 @@ import java.util.List;
 public class ArrayOfArrayOfNumberOnly {
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_NUMBER)
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 24eacf53013..f8adf8e89c4 100644
--- a/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -33,7 +33,7 @@ import java.util.List;
 public class ArrayOfNumberOnly {
   public static final String SERIALIZED_NAME_ARRAY_NUMBER = "ArrayNumber";
   @SerializedName(SERIALIZED_NAME_ARRAY_NUMBER)
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/ArrayTest.java
index a6c287390c8..112ec07fe10 100644
--- a/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -33,15 +33,15 @@ import org.openapitools.client.model.ReadOnlyFirst;
 public class ArrayTest {
   public static final String SERIALIZED_NAME_ARRAY_OF_STRING = "array_of_string";
   @SerializedName(SERIALIZED_NAME_ARRAY_OF_STRING)
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_OF_INTEGER)
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
   @SerializedName(SERIALIZED_NAME_ARRAY_ARRAY_OF_MODEL)
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/EnumArrays.java
index ca9b81defcb..f181d912391 100644
--- a/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -130,7 +130,7 @@ public class EnumArrays {
 
   public static final String SERIALIZED_NAME_ARRAY_ENUM = "array_enum";
   @SerializedName(SERIALIZED_NAME_ARRAY_ENUM)
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index ca37946be88..72c9bd874b5 100644
--- a/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -37,7 +37,7 @@ public class FileSchemaTestClass {
 
   public static final String SERIALIZED_NAME_FILES = "files";
   @SerializedName(SERIALIZED_NAME_FILES)
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/Pet.java
index 266d3d941ca..6dae7446a9d 100644
--- a/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/Pet.java
@@ -52,7 +52,7 @@ public class Pet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/XmlItem.java b/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/XmlItem.java
index 97278128bd8..184f09d430d 100644
--- a/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/XmlItem.java
+++ b/samples/client/petstore/java/retrofit2rx3/src/main/java/org/openapitools/client/model/XmlItem.java
@@ -49,7 +49,7 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_WRAPPED_ARRAY = "wrapped_array";
   @SerializedName(SERIALIZED_NAME_WRAPPED_ARRAY)
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAME_STRING = "name_string";
   @SerializedName(SERIALIZED_NAME_NAME_STRING)
@@ -69,11 +69,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_NAME_ARRAY = "name_array";
   @SerializedName(SERIALIZED_NAME_NAME_ARRAY)
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAME_WRAPPED_ARRAY = "name_wrapped_array";
   @SerializedName(SERIALIZED_NAME_NAME_WRAPPED_ARRAY)
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_STRING = "prefix_string";
   @SerializedName(SERIALIZED_NAME_PREFIX_STRING)
@@ -93,11 +93,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_PREFIX_ARRAY = "prefix_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_ARRAY)
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_WRAPPED_ARRAY)
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAMESPACE_STRING = "namespace_string";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_STRING)
@@ -117,11 +117,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_NAMESPACE_ARRAY = "namespace_array";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_ARRAY)
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
   @SerializedName(SERIALIZED_NAME_NAMESPACE_WRAPPED_ARRAY)
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_NS_STRING = "prefix_ns_string";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_STRING)
@@ -141,11 +141,11 @@ public class XmlItem {
 
   public static final String SERIALIZED_NAME_PREFIX_NS_ARRAY = "prefix_ns_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_ARRAY)
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String SERIALIZED_NAME_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
   @SerializedName(SERIALIZED_NAME_PREFIX_NS_WRAPPED_ARRAY)
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem() {
   }
diff --git a/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index fe288f05fd3..0ea3273e6d0 100644
--- a/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 93563735c8e..8ec937d94e4 100644
--- a/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/ArrayTest.java
index 085f248e13c..8e539861d23 100644
--- a/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -38,13 +38,13 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/EnumArrays.java
index f709cd80b8e..905d8f49f49 100644
--- a/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -109,7 +109,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index 94b9aa8c47b..ddff4505b58 100644
--- a/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -40,7 +40,7 @@ public class FileSchemaTestClass {
   private ModelFile _file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/Pet.java
index 15b15e7fb77..aa4b9b43ff5 100644
--- a/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/Pet.java
@@ -57,7 +57,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/XmlItem.java b/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/XmlItem.java
index 98a5a9978b4..0e34303e5ec 100644
--- a/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/XmlItem.java
+++ b/samples/client/petstore/java/vertx-no-nullable/src/main/java/org/openapitools/client/model/XmlItem.java
@@ -76,7 +76,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   public static final String JSON_PROPERTY_WRAPPED_ARRAY = "wrapped_array";
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_STRING = "name_string";
   private String nameString;
@@ -91,10 +91,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   public static final String JSON_PROPERTY_NAME_ARRAY = "name_array";
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_WRAPPED_ARRAY = "name_wrapped_array";
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_STRING = "prefix_string";
   private String prefixString;
@@ -109,10 +109,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   public static final String JSON_PROPERTY_PREFIX_ARRAY = "prefix_array";
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_STRING = "namespace_string";
   private String namespaceString;
@@ -127,10 +127,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   public static final String JSON_PROPERTY_NAMESPACE_ARRAY = "namespace_array";
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_STRING = "prefix_ns_string";
   private String prefixNsString;
@@ -145,10 +145,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   public static final String JSON_PROPERTY_PREFIX_NS_ARRAY = "prefix_ns_array";
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem() {
   }
diff --git a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index fe288f05fd3..0ea3273e6d0 100644
--- a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 93563735c8e..8ec937d94e4 100644
--- a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ArrayTest.java
index 085f248e13c..8e539861d23 100644
--- a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -38,13 +38,13 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/EnumArrays.java
index f709cd80b8e..905d8f49f49 100644
--- a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -109,7 +109,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index 94b9aa8c47b..ddff4505b58 100644
--- a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -40,7 +40,7 @@ public class FileSchemaTestClass {
   private ModelFile _file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/NullableClass.java b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/NullableClass.java
index 59eba1ade73..58c4c2d1bdc 100644
--- a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/NullableClass.java
+++ b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/NullableClass.java
@@ -79,7 +79,7 @@ public class NullableClass extends HashMap<String, Object> {
   private JsonNullable<List<Object>> arrayAndItemsNullableProp = JsonNullable.<List<Object>>undefined();
 
   public static final String JSON_PROPERTY_ARRAY_ITEMS_NULLABLE = "array_items_nullable";
-  private List<Object> arrayItemsNullable;
+  private List<Object> arrayItemsNullable = new ArrayList<>();
 
   public static final String JSON_PROPERTY_OBJECT_NULLABLE_PROP = "object_nullable_prop";
   private JsonNullable<Map<String, Object>> objectNullableProp = JsonNullable.<Map<String, Object>>undefined();
diff --git a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
index 2dc51d40f65..6699a31ae15 100644
--- a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
+++ b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
@@ -49,7 +49,7 @@ public class ObjectWithDeprecatedFields {
   private DeprecatedObject deprecatedRef;
 
   public static final String JSON_PROPERTY_BARS = "bars";
-  private List<String> bars;
+  private List<String> bars = new ArrayList<>();
 
   public ObjectWithDeprecatedFields() {
   }
diff --git a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/Pet.java
index 15b15e7fb77..aa4b9b43ff5 100644
--- a/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/vertx/src/main/java/org/openapitools/client/model/Pet.java
@@ -57,7 +57,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index da86fbad5f7..85f6ae96c1d 100644
--- a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @jakarta.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index 33c0c0ea9c3..dfbc26116ae 100644
--- a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @jakarta.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() {
   }
diff --git a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ArrayTest.java
index b5b3c2c61a4..5898dd6e96c 100644
--- a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -38,13 +38,13 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @jakarta.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() {
   }
diff --git a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/EnumArrays.java
index b9088e4e9ef..c75845c54dd 100644
--- a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -109,7 +109,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() {
   }
diff --git a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index 4c94fe3be56..37b2ab7a40f 100644
--- a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -40,7 +40,7 @@ public class FileSchemaTestClass {
   private ModelFile _file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() {
   }
diff --git a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/NullableClass.java b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/NullableClass.java
index 48dd74757ae..c011ff87021 100644
--- a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/NullableClass.java
+++ b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/NullableClass.java
@@ -79,7 +79,7 @@ public class NullableClass extends HashMap<String, Object> {
   private JsonNullable<List<Object>> arrayAndItemsNullableProp = JsonNullable.<List<Object>>undefined();
 
   public static final String JSON_PROPERTY_ARRAY_ITEMS_NULLABLE = "array_items_nullable";
-  private List<Object> arrayItemsNullable;
+  private List<Object> arrayItemsNullable = new ArrayList<>();
 
   public static final String JSON_PROPERTY_OBJECT_NULLABLE_PROP = "object_nullable_prop";
   private JsonNullable<Map<String, Object>> objectNullableProp = JsonNullable.<Map<String, Object>>undefined();
diff --git a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
index de38af89c39..7f559434a6f 100644
--- a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
+++ b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
@@ -49,7 +49,7 @@ public class ObjectWithDeprecatedFields {
   private DeprecatedObject deprecatedRef;
 
   public static final String JSON_PROPERTY_BARS = "bars";
-  private List<String> bars;
+  private List<String> bars = new ArrayList<>();
 
   public ObjectWithDeprecatedFields() {
   }
diff --git a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/Pet.java b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/Pet.java
index 1b36c41b4ef..fbc1f5266b7 100644
--- a/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/client/petstore/java/webclient-jakarta/src/main/java/org/openapitools/client/model/Pet.java
@@ -57,7 +57,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/jaxrs-cxf-client-jackson/src/gen/java/org/openapitools/model/Pet.java b/samples/client/petstore/jaxrs-cxf-client-jackson/src/gen/java/org/openapitools/model/Pet.java
index 539ef8a6722..4b8f9a1b9e6 100644
--- a/samples/client/petstore/jaxrs-cxf-client-jackson/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/client/petstore/jaxrs-cxf-client-jackson/src/gen/java/org/openapitools/model/Pet.java
@@ -33,7 +33,7 @@ public class Pet  {
   private List<String> photoUrls = new ArrayList<>();
 
   @ApiModelProperty(value = "")
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
 public enum StatusEnum {
 
diff --git a/samples/client/petstore/jaxrs-cxf-client/src/gen/java/org/openapitools/model/Pet.java b/samples/client/petstore/jaxrs-cxf-client/src/gen/java/org/openapitools/model/Pet.java
index d9bc1cbd197..73502e93895 100644
--- a/samples/client/petstore/jaxrs-cxf-client/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/client/petstore/jaxrs-cxf-client/src/gen/java/org/openapitools/model/Pet.java
@@ -31,7 +31,7 @@ public class Pet  {
   private List<String> photoUrls = new ArrayList<>();
 
   @ApiModelProperty(value = "")
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
 public enum StatusEnum {
 
diff --git a/samples/client/petstore/spring-cloud-deprecated/src/main/java/org/openapitools/model/Pet.java b/samples/client/petstore/spring-cloud-deprecated/src/main/java/org/openapitools/model/Pet.java
index c1ab4231429..32b231a3d92 100644
--- a/samples/client/petstore/spring-cloud-deprecated/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/client/petstore/spring-cloud-deprecated/src/main/java/org/openapitools/model/Pet.java
@@ -39,7 +39,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/spring-cloud-feign-without-url/src/main/java/org/openapitools/model/Pet.java b/samples/client/petstore/spring-cloud-feign-without-url/src/main/java/org/openapitools/model/Pet.java
index 516fff70474..dce6a41f893 100644
--- a/samples/client/petstore/spring-cloud-feign-without-url/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/client/petstore/spring-cloud-feign-without-url/src/main/java/org/openapitools/model/Pet.java
@@ -39,7 +39,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/spring-cloud-tags/src/main/java/org/openapitools/model/Pet.java b/samples/client/petstore/spring-cloud-tags/src/main/java/org/openapitools/model/Pet.java
index a199dffd761..a590ba13cd8 100644
--- a/samples/client/petstore/spring-cloud-tags/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/client/petstore/spring-cloud-tags/src/main/java/org/openapitools/model/Pet.java
@@ -39,7 +39,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/spring-cloud/src/main/java/org/openapitools/model/Pet.java b/samples/client/petstore/spring-cloud/src/main/java/org/openapitools/model/Pet.java
index 516fff70474..dce6a41f893 100644
--- a/samples/client/petstore/spring-cloud/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/client/petstore/spring-cloud/src/main/java/org/openapitools/model/Pet.java
@@ -39,7 +39,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index fc0f2b39c59..bb293adeb26 100644
--- a/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -24,7 +24,7 @@ import jakarta.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index b8539ec6c34..3938cb0b344 100644
--- a/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -24,7 +24,7 @@ import jakarta.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/ArrayTest.java b/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/ArrayTest.java
index 7d139da059b..1b7d301c062 100644
--- a/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/ArrayTest.java
@@ -24,13 +24,13 @@ import jakarta.annotation.Generated;
 public class ArrayTest {
 
   
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/EnumArrays.java b/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/EnumArrays.java
index 8018c9df437..d772edd7d9a 100644
--- a/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/EnumArrays.java
@@ -96,7 +96,7 @@ public class EnumArrays {
   }
 
   
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index f2875149902..b9f108c50c8 100644
--- a/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -26,7 +26,7 @@ public class FileSchemaTestClass {
   private File file;
 
   
-  private List<File> files;
+  private List<File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/Pet.java b/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/Pet.java
index f68404620b1..2611fff4cac 100644
--- a/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/Pet.java
@@ -38,7 +38,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/XmlItem.java b/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/XmlItem.java
index f54d493d6c7..8c2bd613a72 100644
--- a/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/client/petstore/spring-http-interface-reactive/src/main/java/org/openapitools/model/XmlItem.java
@@ -32,7 +32,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -43,10 +43,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -57,10 +57,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -71,10 +71,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -85,10 +85,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnlyDto.java b/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnlyDto.java
index 03223d3009d..66662ef56d3 100644
--- a/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnlyDto.java
+++ b/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnlyDto.java
@@ -26,7 +26,7 @@ import jakarta.annotation.Generated;
 public class ArrayOfArrayOfNumberOnlyDto {
 
   
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnlyDto arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/ArrayOfNumberOnlyDto.java b/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/ArrayOfNumberOnlyDto.java
index 4683178b181..06faba306d6 100644
--- a/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/ArrayOfNumberOnlyDto.java
+++ b/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/ArrayOfNumberOnlyDto.java
@@ -26,7 +26,7 @@ import jakarta.annotation.Generated;
 public class ArrayOfNumberOnlyDto {
 
   
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnlyDto arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/ArrayTestDto.java b/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/ArrayTestDto.java
index 192b3f90dc4..b60ab0c13b5 100644
--- a/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/ArrayTestDto.java
+++ b/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/ArrayTestDto.java
@@ -26,13 +26,13 @@ import jakarta.annotation.Generated;
 public class ArrayTestDto {
 
   
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   
-  private List<List<ReadOnlyFirstDto>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirstDto>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTestDto arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/EnumArraysDto.java b/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/EnumArraysDto.java
index 0e6d8e5ddf4..f3bb2f7e8ec 100644
--- a/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/EnumArraysDto.java
+++ b/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/EnumArraysDto.java
@@ -98,7 +98,7 @@ public class EnumArraysDto {
   }
 
   
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArraysDto justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/FileSchemaTestClassDto.java b/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/FileSchemaTestClassDto.java
index dae42841d4f..6b79a9f969d 100644
--- a/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/FileSchemaTestClassDto.java
+++ b/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/FileSchemaTestClassDto.java
@@ -28,7 +28,7 @@ public class FileSchemaTestClassDto {
   private FileDto file;
 
   
-  private List<FileDto> files;
+  private List<FileDto> files = new ArrayList<>();
 
   public FileSchemaTestClassDto file(FileDto file) {
     this.file = file;
diff --git a/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/PetDto.java b/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/PetDto.java
index ca58796627e..b1c3dd41221 100644
--- a/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/PetDto.java
+++ b/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/PetDto.java
@@ -40,7 +40,7 @@ public class PetDto {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   
-  private List<TagDto> tags;
+  private List<TagDto> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/XmlItemDto.java b/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/XmlItemDto.java
index 19c40f41f9a..f6f733ee063 100644
--- a/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/XmlItemDto.java
+++ b/samples/client/petstore/spring-http-interface/src/main/java/org/openapitools/model/XmlItemDto.java
@@ -34,7 +34,7 @@ public class XmlItemDto {
   private Boolean attributeBoolean;
 
   
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -45,10 +45,10 @@ public class XmlItemDto {
   private Boolean nameBoolean;
 
   
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -59,10 +59,10 @@ public class XmlItemDto {
   private Boolean prefixBoolean;
 
   
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -73,10 +73,10 @@ public class XmlItemDto {
   private Boolean namespaceBoolean;
 
   
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -87,10 +87,10 @@ public class XmlItemDto {
   private Boolean prefixNsBoolean;
 
   
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItemDto attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/openapi3/client/petstore/java/jersey2-java8-swagger1/src/main/java/org/openapitools/client/model/Pet.java b/samples/openapi3/client/petstore/java/jersey2-java8-swagger1/src/main/java/org/openapitools/client/model/Pet.java
index 375c017e2a5..4f660dc5aa8 100644
--- a/samples/openapi3/client/petstore/java/jersey2-java8-swagger1/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/openapi3/client/petstore/java/jersey2-java8-swagger1/src/main/java/org/openapitools/client/model/Pet.java
@@ -59,7 +59,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/client/petstore/java/jersey2-java8-swagger2/src/main/java/org/openapitools/client/model/Pet.java b/samples/openapi3/client/petstore/java/jersey2-java8-swagger2/src/main/java/org/openapitools/client/model/Pet.java
index d0f9bbc9f69..3795fd24e06 100644
--- a/samples/openapi3/client/petstore/java/jersey2-java8-swagger2/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/openapi3/client/petstore/java/jersey2-java8-swagger2/src/main/java/org/openapitools/client/model/Pet.java
@@ -58,7 +58,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
index efff0de5d11..15863dc3389 100644
--- a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
@@ -38,7 +38,7 @@ import org.openapitools.client.JSON;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly() { 
   }
diff --git a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
index a4c81969a86..a06f9bb8876 100644
--- a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+++ b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
@@ -38,7 +38,7 @@ import org.openapitools.client.JSON;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly() { 
   }
diff --git a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayTest.java b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayTest.java
index 3c45dfb980b..2f8ed7a52b0 100644
--- a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayTest.java
+++ b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ArrayTest.java
@@ -40,13 +40,13 @@ import org.openapitools.client.JSON;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest() { 
   }
diff --git a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/Drawing.java b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/Drawing.java
index 26bc73ac477..5bece787be3 100644
--- a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/Drawing.java
+++ b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/Drawing.java
@@ -61,7 +61,7 @@ public class Drawing {
   private JsonNullable<NullableShape> nullableShape = JsonNullable.<NullableShape>undefined();
 
   public static final String JSON_PROPERTY_SHAPES = "shapes";
-  private List<Shape> shapes;
+  private List<Shape> shapes = new ArrayList<>();
 
   public Drawing() { 
   }
diff --git a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/EnumArrays.java b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/EnumArrays.java
index f6ebb1453b3..faa32a79a58 100644
--- a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/EnumArrays.java
+++ b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/EnumArrays.java
@@ -111,7 +111,7 @@ public class EnumArrays {
   }
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays() { 
   }
diff --git a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
index a5a2fd172b1..2c1bb74d31f 100644
--- a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+++ b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
@@ -42,7 +42,7 @@ public class FileSchemaTestClass {
   private ModelFile _file;
 
   public static final String JSON_PROPERTY_FILES = "files";
-  private List<ModelFile> files;
+  private List<ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass() { 
   }
diff --git a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/NullableClass.java b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/NullableClass.java
index 7b2dfb01bf5..3ac465f8561 100644
--- a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/NullableClass.java
+++ b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/NullableClass.java
@@ -85,7 +85,7 @@ public class NullableClass {
   private JsonNullable<List<Object>> arrayAndItemsNullableProp = JsonNullable.<List<Object>>undefined();
 
   public static final String JSON_PROPERTY_ARRAY_ITEMS_NULLABLE = "array_items_nullable";
-  private List<Object> arrayItemsNullable;
+  private List<Object> arrayItemsNullable = new ArrayList<>();
 
   public static final String JSON_PROPERTY_OBJECT_NULLABLE_PROP = "object_nullable_prop";
   private JsonNullable<Map<String, Object>> objectNullableProp = JsonNullable.<Map<String, Object>>undefined();
diff --git a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
index 86a6393aa31..872f9734a9d 100644
--- a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
+++ b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
@@ -51,7 +51,7 @@ public class ObjectWithDeprecatedFields {
   private DeprecatedObject deprecatedRef;
 
   public static final String JSON_PROPERTY_BARS = "bars";
-  private List<String> bars;
+  private List<String> bars = new ArrayList<>();
 
   public ObjectWithDeprecatedFields() { 
   }
diff --git a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/Pet.java b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/Pet.java
index 701d0e570a1..e32ee8dbb48 100644
--- a/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/Pet.java
+++ b/samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/Pet.java
@@ -56,7 +56,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/client/petstore/spring-cloud-3-with-optional/src/main/java/org/openapitools/model/Pet.java b/samples/openapi3/client/petstore/spring-cloud-3-with-optional/src/main/java/org/openapitools/model/Pet.java
index 4b3df7081dc..86ff182e24d 100644
--- a/samples/openapi3/client/petstore/spring-cloud-3-with-optional/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/openapi3/client/petstore/spring-cloud-3-with-optional/src/main/java/org/openapitools/model/Pet.java
@@ -36,7 +36,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/client/petstore/spring-cloud-3/src/main/java/org/openapitools/model/Pet.java b/samples/openapi3/client/petstore/spring-cloud-3/src/main/java/org/openapitools/model/Pet.java
index 22f7fd71d0c..81a1f0495ee 100644
--- a/samples/openapi3/client/petstore/spring-cloud-3/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/openapi3/client/petstore/spring-cloud-3/src/main/java/org/openapitools/model/Pet.java
@@ -38,7 +38,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/client/petstore/spring-cloud-async/src/main/java/org/openapitools/model/Pet.java b/samples/openapi3/client/petstore/spring-cloud-async/src/main/java/org/openapitools/model/Pet.java
index 7e02f2f209f..4aa7bc36bb7 100644
--- a/samples/openapi3/client/petstore/spring-cloud-async/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/openapi3/client/petstore/spring-cloud-async/src/main/java/org/openapitools/model/Pet.java
@@ -38,7 +38,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/client/petstore/spring-cloud-http-basic/src/main/java/org/openapitools/model/Pet.java b/samples/openapi3/client/petstore/spring-cloud-http-basic/src/main/java/org/openapitools/model/Pet.java
index 7e02f2f209f..4aa7bc36bb7 100644
--- a/samples/openapi3/client/petstore/spring-cloud-http-basic/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/openapi3/client/petstore/spring-cloud-http-basic/src/main/java/org/openapitools/model/Pet.java
@@ -38,7 +38,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index 5d9620a9662..a07b9f5f5f8 100644
--- a/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -26,7 +26,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index deabc1c65e6..4513ec53877 100644
--- a/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -26,7 +26,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/ArrayTest.java b/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/ArrayTest.java
index 39be54311c7..3ea26158c18 100644
--- a/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/ArrayTest.java
@@ -26,13 +26,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/EnumArrays.java b/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/EnumArrays.java
index 46bf4157bde..d994343e973 100644
--- a/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/EnumArrays.java
@@ -98,7 +98,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index c5a92f52cff..e8a3362e07e 100644
--- a/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -28,7 +28,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/Pet.java b/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/Pet.java
index 8ec5b95ef4a..3f558ab5e63 100644
--- a/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/Pet.java
@@ -40,7 +40,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/XmlItem.java b/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/XmlItem.java
index 344d0d98546..eccca3318bf 100644
--- a/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/openapi3/client/petstore/spring-cloud-oas3-fakeapi/src/main/java/org/openapitools/model/XmlItem.java
@@ -34,7 +34,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -45,10 +45,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -59,10 +59,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -73,10 +73,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -87,10 +87,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/openapi3/client/petstore/spring-cloud-spring-pageable/src/main/java/org/openapitools/model/Pet.java b/samples/openapi3/client/petstore/spring-cloud-spring-pageable/src/main/java/org/openapitools/model/Pet.java
index f00c66c8e83..1c5821020e1 100644
--- a/samples/openapi3/client/petstore/spring-cloud-spring-pageable/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/openapi3/client/petstore/spring-cloud-spring-pageable/src/main/java/org/openapitools/model/Pet.java
@@ -38,7 +38,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/client/petstore/spring-cloud/src/main/java/org/openapitools/model/Pet.java b/samples/openapi3/client/petstore/spring-cloud/src/main/java/org/openapitools/model/Pet.java
index 7e02f2f209f..4aa7bc36bb7 100644
--- a/samples/openapi3/client/petstore/spring-cloud/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/openapi3/client/petstore/spring-cloud/src/main/java/org/openapitools/model/Pet.java
@@ -38,7 +38,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/client/petstore/spring-stubs-skip-default-interface/src/main/java/org/openapitools/model/Pet.java b/samples/openapi3/client/petstore/spring-stubs-skip-default-interface/src/main/java/org/openapitools/model/Pet.java
index 7e02f2f209f..4aa7bc36bb7 100644
--- a/samples/openapi3/client/petstore/spring-stubs-skip-default-interface/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/openapi3/client/petstore/spring-stubs-skip-default-interface/src/main/java/org/openapitools/model/Pet.java
@@ -38,7 +38,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/client/petstore/spring-stubs/src/main/java/org/openapitools/model/Pet.java b/samples/openapi3/client/petstore/spring-stubs/src/main/java/org/openapitools/model/Pet.java
index 7e02f2f209f..4aa7bc36bb7 100644
--- a/samples/openapi3/client/petstore/spring-stubs/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/openapi3/client/petstore/spring-stubs/src/main/java/org/openapitools/model/Pet.java
@@ -38,7 +38,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/server/petstore/spring-boot-springdoc/src/main/java/org/openapitools/model/Pet.java b/samples/openapi3/server/petstore/spring-boot-springdoc/src/main/java/org/openapitools/model/Pet.java
index 7e02f2f209f..4aa7bc36bb7 100644
--- a/samples/openapi3/server/petstore/spring-boot-springdoc/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/openapi3/server/petstore/spring-boot-springdoc/src/main/java/org/openapitools/model/Pet.java
@@ -38,7 +38,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/server/petstore/springboot-3/src/main/java/org/openapitools/model/Pet.java b/samples/openapi3/server/petstore/springboot-3/src/main/java/org/openapitools/model/Pet.java
index 693d6e12c51..f10ebeeb11a 100644
--- a/samples/openapi3/server/petstore/springboot-3/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/openapi3/server/petstore/springboot-3/src/main/java/org/openapitools/model/Pet.java
@@ -45,7 +45,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index 5d9620a9662..a07b9f5f5f8 100644
--- a/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -26,7 +26,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index deabc1c65e6..4513ec53877 100644
--- a/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -26,7 +26,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayTest.java b/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayTest.java
index 39be54311c7..3ea26158c18 100644
--- a/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayTest.java
@@ -26,13 +26,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/EnumArrays.java b/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/EnumArrays.java
index 46bf4157bde..d994343e973 100644
--- a/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/EnumArrays.java
@@ -98,7 +98,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index c5a92f52cff..e8a3362e07e 100644
--- a/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -28,7 +28,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/Pet.java b/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/Pet.java
index bd36429fabc..5d5fd678a93 100644
--- a/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/Pet.java
@@ -40,7 +40,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/XmlItem.java b/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/XmlItem.java
index 344d0d98546..eccca3318bf 100644
--- a/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/openapi3/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/XmlItem.java
@@ -34,7 +34,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -45,10 +45,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -59,10 +59,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -73,10 +73,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -87,10 +87,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index 5d9620a9662..a07b9f5f5f8 100644
--- a/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -26,7 +26,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index deabc1c65e6..4513ec53877 100644
--- a/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -26,7 +26,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayTest.java b/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayTest.java
index 39be54311c7..3ea26158c18 100644
--- a/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayTest.java
@@ -26,13 +26,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/EnumArrays.java b/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/EnumArrays.java
index 46bf4157bde..d994343e973 100644
--- a/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/EnumArrays.java
@@ -98,7 +98,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index c5a92f52cff..e8a3362e07e 100644
--- a/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -28,7 +28,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/Pet.java b/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/Pet.java
index bd36429fabc..5d5fd678a93 100644
--- a/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/Pet.java
@@ -40,7 +40,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/XmlItem.java b/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/XmlItem.java
index 344d0d98546..eccca3318bf 100644
--- a/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/openapi3/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/XmlItem.java
@@ -34,7 +34,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -45,10 +45,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -59,10 +59,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -73,10 +73,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -87,10 +87,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/openapi3/server/petstore/springboot-source/src/main/java/org/openapitools/model/Pet.java b/samples/openapi3/server/petstore/springboot-source/src/main/java/org/openapitools/model/Pet.java
index 824c742e32f..c7857b3392a 100644
--- a/samples/openapi3/server/petstore/springboot-source/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/openapi3/server/petstore/springboot-source/src/main/java/org/openapitools/model/Pet.java
@@ -36,7 +36,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/openapi3/server/petstore/springboot/src/main/java/org/openapitools/model/Pet.java b/samples/openapi3/server/petstore/springboot/src/main/java/org/openapitools/model/Pet.java
index 7e02f2f209f..4aa7bc36bb7 100644
--- a/samples/openapi3/server/petstore/springboot/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/openapi3/server/petstore/springboot/src/main/java/org/openapitools/model/Pet.java
@@ -38,7 +38,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/java-camel/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/java-camel/src/main/java/org/openapitools/model/Pet.java
index 610bfbee61f..df664a84a0a 100644
--- a/samples/server/petstore/java-camel/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/java-camel/src/main/java/org/openapitools/model/Pet.java
@@ -46,7 +46,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ArrayOfArrayOfNumberOnly.java
index dab2aafb6ad..83c75a242e8 100644
--- a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ArrayOfArrayOfNumberOnly.java
@@ -11,7 +11,7 @@ import jakarta.validation.Valid;
 
 public class ArrayOfArrayOfNumberOnly   {
 
-    private List<List<BigDecimal>> arrayArrayNumber;
+    private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
     /**
      * Default constructor.
diff --git a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ArrayOfNumberOnly.java b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ArrayOfNumberOnly.java
index 96ff5ea0a44..971fb516ba0 100644
--- a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ArrayOfNumberOnly.java
@@ -11,7 +11,7 @@ import jakarta.validation.Valid;
 
 public class ArrayOfNumberOnly   {
 
-    private List<BigDecimal> arrayNumber;
+    private List<BigDecimal> arrayNumber = new ArrayList<>();
 
     /**
      * Default constructor.
diff --git a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ArrayTest.java b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ArrayTest.java
index 8112ec19d48..d94cad1da9a 100644
--- a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ArrayTest.java
+++ b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ArrayTest.java
@@ -11,9 +11,9 @@ import jakarta.validation.Valid;
 
 public class ArrayTest   {
 
-    private List<String> arrayOfString;
-    private List<List<Long>> arrayArrayOfInteger;
-    private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+    private List<String> arrayOfString = new ArrayList<>();
+    private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
+    private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
     /**
      * Default constructor.
diff --git a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/EnumArrays.java b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/EnumArrays.java
index ba6203947fe..29d6ebaa8fb 100644
--- a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/EnumArrays.java
+++ b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/EnumArrays.java
@@ -87,7 +87,7 @@ public class EnumArrays   {
     }
 
 
-    private List<ArrayEnumEnum> arrayEnum;
+    private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
     /**
      * Default constructor.
diff --git a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/FileSchemaTestClass.java b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/FileSchemaTestClass.java
index 34fbdce5ca9..2b6964db9de 100644
--- a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/FileSchemaTestClass.java
@@ -12,7 +12,7 @@ import jakarta.validation.Valid;
 public class FileSchemaTestClass   {
 
     private ModelFile _file;
-    private List<@Valid ModelFile> files;
+    private List<@Valid ModelFile> files = new ArrayList<>();
 
     /**
      * Default constructor.
diff --git a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/NullableClass.java b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/NullableClass.java
index fa9e97a3c05..11e7e2ec0fd 100644
--- a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/NullableClass.java
+++ b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/NullableClass.java
@@ -24,7 +24,7 @@ public class NullableClass extends HashMap<String, Object>  {
     private OffsetDateTime datetimeProp;
     private List<Object> arrayNullableProp;
     private List<Object> arrayAndItemsNullableProp;
-    private List<Object> arrayItemsNullable;
+    private List<Object> arrayItemsNullable = new ArrayList<>();
     private Map<String, Object> objectNullableProp;
     private Map<String, Object> objectAndItemsNullableProp;
     private Map<String, Object> objectItemsNullable = new HashMap<>();
diff --git a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ObjectWithDeprecatedFields.java b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ObjectWithDeprecatedFields.java
index e66eb43c911..83bc634c1d6 100644
--- a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ObjectWithDeprecatedFields.java
+++ b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/ObjectWithDeprecatedFields.java
@@ -15,7 +15,7 @@ public class ObjectWithDeprecatedFields   {
     private String uuid;
     private BigDecimal id;
     private DeprecatedObject deprecatedRef;
-    private List<String> bars;
+    private List<String> bars = new ArrayList<>();
 
     /**
      * Default constructor.
diff --git a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/Pet.java b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/Pet.java
index 17dd8d5f517..671a9be156d 100644
--- a/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/Pet.java
+++ b/samples/server/petstore/java-helidon-server/se/src/main/java/org/openapitools/server/model/Pet.java
@@ -21,7 +21,7 @@ public class Pet   {
     private Category category;
     private String name;
     private Set<String> photoUrls = new LinkedHashSet<>();
-    private List<@Valid Tag> tags;
+    private List<@Valid Tag> tags = new ArrayList<>();
 
     /**
     * pet status in the store
diff --git a/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index 19c839109af..2a9a3233c79 100644
--- a/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -25,7 +25,7 @@ public class ArrayOfArrayOfNumberOnly   {
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
     if (this.arrayArrayNumber == null) {
-      this.arrayArrayNumber = ;
+      this.arrayArrayNumber = new ArrayList<>();
     }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
diff --git a/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
index 7e6609a26b6..bc7d536da54 100644
--- a/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -25,7 +25,7 @@ public class ArrayOfNumberOnly   {
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
     if (this.arrayNumber == null) {
-      this.arrayNumber = ;
+      this.arrayNumber = new ArrayList<>();
     }
     this.arrayNumber.add(arrayNumberItem);
     return this;
diff --git a/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/ArrayTest.java
index 8c9822ff1e3..b8a2be47914 100644
--- a/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/ArrayTest.java
@@ -31,7 +31,7 @@ public class ArrayTest   {
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
     if (this.arrayOfString == null) {
-      this.arrayOfString = ;
+      this.arrayOfString = new ArrayList<>();
     }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
@@ -57,7 +57,7 @@ public class ArrayTest   {
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
     if (this.arrayArrayOfInteger == null) {
-      this.arrayArrayOfInteger = ;
+      this.arrayArrayOfInteger = new ArrayList<>();
     }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
@@ -83,7 +83,7 @@ public class ArrayTest   {
 
   public ArrayTest addArrayArrayOfModelItem(List<@Valid ReadOnlyFirst> arrayArrayOfModelItem) {
     if (this.arrayArrayOfModel == null) {
-      this.arrayArrayOfModel = ;
+      this.arrayArrayOfModel = new ArrayList<>();
     }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
diff --git a/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/EnumArrays.java
index a2c713270f5..17171d8f7ed 100644
--- a/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/EnumArrays.java
@@ -108,7 +108,7 @@ public class EnumArrays   {
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
     if (this.arrayEnum == null) {
-      this.arrayEnum = ;
+      this.arrayEnum = new ArrayList<>();
     }
     this.arrayEnum.add(arrayEnumItem);
     return this;
diff --git a/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
index d9c58dd116a..30b77e3d179 100644
--- a/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
@@ -46,7 +46,7 @@ public class FileSchemaTestClass   {
 
   public FileSchemaTestClass addFilesItem(ModelFile filesItem) {
     if (this.files == null) {
-      this.files = ;
+      this.files = new ArrayList<>();
     }
     this.files.add(filesItem);
     return this;
diff --git a/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/Pet.java
index d1b78fa3eb2..325b018cd88 100644
--- a/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/Pet.java
@@ -156,7 +156,7 @@ public class Pet   {
 
   public Pet addTagsItem(Tag tagsItem) {
     if (this.tags == null) {
-      this.tags = ;
+      this.tags = new ArrayList<>();
     }
     this.tags.add(tagsItem);
     return this;
diff --git a/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/XmlItem.java
index 7cf083a8d39..abcd9fd183c 100644
--- a/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/java-msf4j/src/gen/java/org/openapitools/model/XmlItem.java
@@ -181,7 +181,7 @@ public class XmlItem   {
 
   public XmlItem addWrappedArrayItem(Integer wrappedArrayItem) {
     if (this.wrappedArray == null) {
-      this.wrappedArray = ;
+      this.wrappedArray = new ArrayList<>();
     }
     this.wrappedArray.add(wrappedArrayItem);
     return this;
@@ -279,7 +279,7 @@ public class XmlItem   {
 
   public XmlItem addNameArrayItem(Integer nameArrayItem) {
     if (this.nameArray == null) {
-      this.nameArray = ;
+      this.nameArray = new ArrayList<>();
     }
     this.nameArray.add(nameArrayItem);
     return this;
@@ -305,7 +305,7 @@ public class XmlItem   {
 
   public XmlItem addNameWrappedArrayItem(Integer nameWrappedArrayItem) {
     if (this.nameWrappedArray == null) {
-      this.nameWrappedArray = ;
+      this.nameWrappedArray = new ArrayList<>();
     }
     this.nameWrappedArray.add(nameWrappedArrayItem);
     return this;
@@ -403,7 +403,7 @@ public class XmlItem   {
 
   public XmlItem addPrefixArrayItem(Integer prefixArrayItem) {
     if (this.prefixArray == null) {
-      this.prefixArray = ;
+      this.prefixArray = new ArrayList<>();
     }
     this.prefixArray.add(prefixArrayItem);
     return this;
@@ -429,7 +429,7 @@ public class XmlItem   {
 
   public XmlItem addPrefixWrappedArrayItem(Integer prefixWrappedArrayItem) {
     if (this.prefixWrappedArray == null) {
-      this.prefixWrappedArray = ;
+      this.prefixWrappedArray = new ArrayList<>();
     }
     this.prefixWrappedArray.add(prefixWrappedArrayItem);
     return this;
@@ -527,7 +527,7 @@ public class XmlItem   {
 
   public XmlItem addNamespaceArrayItem(Integer namespaceArrayItem) {
     if (this.namespaceArray == null) {
-      this.namespaceArray = ;
+      this.namespaceArray = new ArrayList<>();
     }
     this.namespaceArray.add(namespaceArrayItem);
     return this;
@@ -553,7 +553,7 @@ public class XmlItem   {
 
   public XmlItem addNamespaceWrappedArrayItem(Integer namespaceWrappedArrayItem) {
     if (this.namespaceWrappedArray == null) {
-      this.namespaceWrappedArray = ;
+      this.namespaceWrappedArray = new ArrayList<>();
     }
     this.namespaceWrappedArray.add(namespaceWrappedArrayItem);
     return this;
@@ -651,7 +651,7 @@ public class XmlItem   {
 
   public XmlItem addPrefixNsArrayItem(Integer prefixNsArrayItem) {
     if (this.prefixNsArray == null) {
-      this.prefixNsArray = ;
+      this.prefixNsArray = new ArrayList<>();
     }
     this.prefixNsArray.add(prefixNsArrayItem);
     return this;
@@ -677,7 +677,7 @@ public class XmlItem   {
 
   public XmlItem addPrefixNsWrappedArrayItem(Integer prefixNsWrappedArrayItem) {
     if (this.prefixNsWrappedArray == null) {
-      this.prefixNsWrappedArray = ;
+      this.prefixNsWrappedArray = new ArrayList<>();
     }
     this.prefixNsWrappedArray.add(prefixNsWrappedArrayItem);
     return this;
diff --git a/samples/server/petstore/java-undertow/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/java-undertow/src/main/java/org/openapitools/model/Pet.java
index e80d06b5131..2df17cf2689 100644
--- a/samples/server/petstore/java-undertow/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/java-undertow/src/main/java/org/openapitools/model/Pet.java
@@ -36,7 +36,7 @@ public class Pet   {
   private Category category;
   private String name;
   private List<String> photoUrls = new ArrayList<>();
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
 
   public enum StatusEnum {
diff --git a/samples/server/petstore/java-vertx-web/src/main/java/org/openapitools/vertxweb/server/model/Pet.java b/samples/server/petstore/java-vertx-web/src/main/java/org/openapitools/vertxweb/server/model/Pet.java
index 748f0320486..7aae8f77aaa 100644
--- a/samples/server/petstore/java-vertx-web/src/main/java/org/openapitools/vertxweb/server/model/Pet.java
+++ b/samples/server/petstore/java-vertx-web/src/main/java/org/openapitools/vertxweb/server/model/Pet.java
@@ -20,7 +20,7 @@ public class Pet   {
   private Category category;
   private String name;
   private List<String> photoUrls = new ArrayList<>();
-  private List<Tag> tags;
+  private List<Tag> tags = new ArrayList<>();
 
 
   public enum StatusEnum {
diff --git a/samples/server/petstore/jaxrs-cxf-annotated-base-path/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-cxf-annotated-base-path/src/gen/java/org/openapitools/model/Pet.java
index 71af8d8a4ce..1d31a77e0ef 100644
--- a/samples/server/petstore/jaxrs-cxf-annotated-base-path/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-cxf-annotated-base-path/src/gen/java/org/openapitools/model/Pet.java
@@ -37,7 +37,7 @@ public class Pet  {
 
   @ApiModelProperty(value = "")
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
 public enum StatusEnum {
 
diff --git a/samples/server/petstore/jaxrs-cxf-cdi/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-cxf-cdi/src/gen/java/org/openapitools/model/Pet.java
index 19625cc472b..1313d9b3b36 100644
--- a/samples/server/petstore/jaxrs-cxf-cdi/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-cxf-cdi/src/gen/java/org/openapitools/model/Pet.java
@@ -31,7 +31,7 @@ public class Pet   {
 
   private List<String> photoUrls = new ArrayList<>();
 
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
 
 public enum StatusEnum {
diff --git a/samples/server/petstore/jaxrs-cxf-non-spring-app/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-cxf-non-spring-app/src/gen/java/org/openapitools/model/Pet.java
index 71af8d8a4ce..1d31a77e0ef 100644
--- a/samples/server/petstore/jaxrs-cxf-non-spring-app/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-cxf-non-spring-app/src/gen/java/org/openapitools/model/Pet.java
@@ -37,7 +37,7 @@ public class Pet  {
 
   @ApiModelProperty(value = "")
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
 public enum StatusEnum {
 
diff --git a/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index 3e877b82d54..35f92b8ebff 100644
--- a/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -16,7 +16,7 @@ public class ArrayOfArrayOfNumberOnly  {
   
   @ApiModelProperty(value = "")
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
  /**
    * Get arrayArrayNumber
    * @return arrayArrayNumber
diff --git a/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
index 6261829241c..63a30578d39 100644
--- a/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -16,7 +16,7 @@ public class ArrayOfNumberOnly  {
   
   @ApiModelProperty(value = "")
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
  /**
    * Get arrayNumber
    * @return arrayNumber
diff --git a/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/ArrayTest.java
index 8ff058a6d4c..78bb8495dfd 100644
--- a/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/ArrayTest.java
@@ -15,15 +15,15 @@ import com.fasterxml.jackson.annotation.JsonProperty;
 public class ArrayTest  {
   
   @ApiModelProperty(value = "")
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @ApiModelProperty(value = "")
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @ApiModelProperty(value = "")
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
  /**
    * Get arrayOfString
    * @return arrayOfString
diff --git a/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/EnumArrays.java
index 10ec68c1a80..5d768ce6b49 100644
--- a/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/EnumArrays.java
@@ -83,7 +83,7 @@ FISH(String.valueOf("fish")), CRAB(String.valueOf("crab"));
 }
 
   @ApiModelProperty(value = "")
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
  /**
    * Get justSymbol
    * @return justSymbol
diff --git a/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
index 14c7478308f..fd7494f4fe1 100644
--- a/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
@@ -20,7 +20,7 @@ public class FileSchemaTestClass  {
 
   @ApiModelProperty(value = "")
   @Valid
-  private List<@Valid ModelFile> files;
+  private List<@Valid ModelFile> files = new ArrayList<>();
  /**
    * Get _file
    * @return _file
diff --git a/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/Pet.java
index f18417662b8..4c2d48fc56f 100644
--- a/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/Pet.java
@@ -35,7 +35,7 @@ public class Pet  {
 
   @ApiModelProperty(value = "")
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
 public enum StatusEnum {
 
diff --git a/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/XmlItem.java
index 09909e88407..94bdf4ef950 100644
--- a/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/jaxrs-cxf/src/gen/java/org/openapitools/model/XmlItem.java
@@ -28,7 +28,7 @@ public class XmlItem  {
   private Boolean attributeBoolean;
 
   @ApiModelProperty(value = "")
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   @ApiModelProperty(example = "string", value = "")
   private String nameString;
@@ -44,10 +44,10 @@ public class XmlItem  {
   private Boolean nameBoolean;
 
   @ApiModelProperty(value = "")
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @ApiModelProperty(value = "")
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   @ApiModelProperty(example = "string", value = "")
   private String prefixString;
@@ -63,10 +63,10 @@ public class XmlItem  {
   private Boolean prefixBoolean;
 
   @ApiModelProperty(value = "")
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @ApiModelProperty(value = "")
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   @ApiModelProperty(example = "string", value = "")
   private String namespaceString;
@@ -82,10 +82,10 @@ public class XmlItem  {
   private Boolean namespaceBoolean;
 
   @ApiModelProperty(value = "")
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @ApiModelProperty(value = "")
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   @ApiModelProperty(example = "string", value = "")
   private String prefixNsString;
@@ -101,10 +101,10 @@ public class XmlItem  {
   private Boolean prefixNsBoolean;
 
   @ApiModelProperty(value = "")
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @ApiModelProperty(value = "")
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
  /**
    * Get attributeString
    * @return attributeString
diff --git a/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index 68c29710a97..a0e6538d239 100644
--- a/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -37,7 +37,7 @@ import javax.validation.Valid;
 public class ArrayOfArrayOfNumberOnly  implements Serializable {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
   @JsonProperty(JSON_PROPERTY_ARRAY_ARRAY_NUMBER)
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
index c8a32216c94..f524e0f7818 100644
--- a/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -37,7 +37,7 @@ import javax.validation.Valid;
 public class ArrayOfNumberOnly  implements Serializable {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
   @JsonProperty(JSON_PROPERTY_ARRAY_NUMBER)
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/ArrayTest.java
index e406a56fac9..ad5e94bb765 100644
--- a/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/ArrayTest.java
@@ -39,15 +39,15 @@ import javax.validation.Valid;
 public class ArrayTest  implements Serializable {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
   @JsonProperty(JSON_PROPERTY_ARRAY_OF_STRING)
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
   @JsonProperty(JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER)
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
   @JsonProperty(JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL)
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/EnumArrays.java
index b6800249826..f5d790eabf5 100644
--- a/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/EnumArrays.java
@@ -104,7 +104,7 @@ public class EnumArrays  implements Serializable {
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
   @JsonProperty(JSON_PROPERTY_ARRAY_ENUM)
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
index 164cf09b301..25bb5dd795a 100644
--- a/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
@@ -42,7 +42,7 @@ public class FileSchemaTestClass  implements Serializable {
 
   public static final String JSON_PROPERTY_FILES = "files";
   @JsonProperty(JSON_PROPERTY_FILES)
-  private List<@Valid ModelFile> files;
+  private List<@Valid ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass _file(ModelFile _file) {
     this._file = _file;
diff --git a/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/Pet.java
index 17885e6fac0..bf4db08b768 100644
--- a/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/Pet.java
@@ -63,7 +63,7 @@ public class Pet  implements Serializable {
 
   public static final String JSON_PROPERTY_TAGS = "tags";
   @JsonProperty(JSON_PROPERTY_TAGS)
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/XmlItem.java
index d92640f1b65..7184a3aefce 100644
--- a/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/jaxrs-datelib-j8/src/gen/java/org/openapitools/model/XmlItem.java
@@ -81,7 +81,7 @@ public class XmlItem  implements Serializable {
 
   public static final String JSON_PROPERTY_WRAPPED_ARRAY = "wrapped_array";
   @JsonProperty(JSON_PROPERTY_WRAPPED_ARRAY)
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_STRING = "name_string";
   @JsonProperty(JSON_PROPERTY_NAME_STRING)
@@ -101,11 +101,11 @@ public class XmlItem  implements Serializable {
 
   public static final String JSON_PROPERTY_NAME_ARRAY = "name_array";
   @JsonProperty(JSON_PROPERTY_NAME_ARRAY)
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_WRAPPED_ARRAY = "name_wrapped_array";
   @JsonProperty(JSON_PROPERTY_NAME_WRAPPED_ARRAY)
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_STRING = "prefix_string";
   @JsonProperty(JSON_PROPERTY_PREFIX_STRING)
@@ -125,11 +125,11 @@ public class XmlItem  implements Serializable {
 
   public static final String JSON_PROPERTY_PREFIX_ARRAY = "prefix_array";
   @JsonProperty(JSON_PROPERTY_PREFIX_ARRAY)
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
   @JsonProperty(JSON_PROPERTY_PREFIX_WRAPPED_ARRAY)
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_STRING = "namespace_string";
   @JsonProperty(JSON_PROPERTY_NAMESPACE_STRING)
@@ -149,11 +149,11 @@ public class XmlItem  implements Serializable {
 
   public static final String JSON_PROPERTY_NAMESPACE_ARRAY = "namespace_array";
   @JsonProperty(JSON_PROPERTY_NAMESPACE_ARRAY)
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
   @JsonProperty(JSON_PROPERTY_NAMESPACE_WRAPPED_ARRAY)
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_STRING = "prefix_ns_string";
   @JsonProperty(JSON_PROPERTY_PREFIX_NS_STRING)
@@ -173,11 +173,11 @@ public class XmlItem  implements Serializable {
 
   public static final String JSON_PROPERTY_PREFIX_NS_ARRAY = "prefix_ns_array";
   @JsonProperty(JSON_PROPERTY_PREFIX_NS_ARRAY)
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
   @JsonProperty(JSON_PROPERTY_PREFIX_NS_WRAPPED_ARRAY)
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index 7e1a747d87e..58d71a089b5 100644
--- a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import javax.validation.Valid;
 public class ArrayOfArrayOfNumberOnly   {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
   @JsonProperty(JSON_PROPERTY_ARRAY_ARRAY_NUMBER)
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
index fccb8d855a3..08d8883200f 100644
--- a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import javax.validation.Valid;
 public class ArrayOfNumberOnly   {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
   @JsonProperty(JSON_PROPERTY_ARRAY_NUMBER)
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ArrayTest.java
index b423170dab0..69b4c749239 100644
--- a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ArrayTest.java
@@ -38,15 +38,15 @@ import javax.validation.Valid;
 public class ArrayTest   {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
   @JsonProperty(JSON_PROPERTY_ARRAY_OF_STRING)
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
   @JsonProperty(JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER)
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
   @JsonProperty(JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL)
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/EnumArrays.java
index 23e0cafa0e2..90d11edf7e1 100644
--- a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/EnumArrays.java
@@ -103,7 +103,7 @@ public class EnumArrays   {
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
   @JsonProperty(JSON_PROPERTY_ARRAY_ENUM)
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
index 4de852677f2..d88b0af4857 100644
--- a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
@@ -41,7 +41,7 @@ public class FileSchemaTestClass   {
 
   public static final String JSON_PROPERTY_FILES = "files";
   @JsonProperty(JSON_PROPERTY_FILES)
-  private List<@Valid ModelFile> files;
+  private List<@Valid ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass _file(ModelFile _file) {
     this._file = _file;
diff --git a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/NullableClass.java b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/NullableClass.java
index c5693c944ef..f664994bf09 100644
--- a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/NullableClass.java
+++ b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/NullableClass.java
@@ -82,7 +82,7 @@ public class NullableClass extends HashMap<String, Object>  {
 
   public static final String JSON_PROPERTY_ARRAY_ITEMS_NULLABLE = "array_items_nullable";
   @JsonProperty(JSON_PROPERTY_ARRAY_ITEMS_NULLABLE)
-  private List<Object> arrayItemsNullable;
+  private List<Object> arrayItemsNullable = new ArrayList<>();
 
   public static final String JSON_PROPERTY_OBJECT_NULLABLE_PROP = "object_nullable_prop";
   @JsonProperty(JSON_PROPERTY_OBJECT_NULLABLE_PROP)
diff --git a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ObjectWithDeprecatedFields.java b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ObjectWithDeprecatedFields.java
index bdcd7d0bb31..2e241bc0176 100644
--- a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ObjectWithDeprecatedFields.java
+++ b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/ObjectWithDeprecatedFields.java
@@ -52,7 +52,7 @@ public class ObjectWithDeprecatedFields   {
 
   public static final String JSON_PROPERTY_BARS = "bars";
   @JsonProperty(JSON_PROPERTY_BARS)
-  private List<String> bars;
+  private List<String> bars = new ArrayList<>();
 
   public ObjectWithDeprecatedFields uuid(String uuid) {
     this.uuid = uuid;
diff --git a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/Pet.java
index dc10d3ad53b..116f53a76a1 100644
--- a/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-jersey/src/gen/java/org/openapitools/model/Pet.java
@@ -62,7 +62,7 @@ public class Pet   {
 
   public static final String JSON_PROPERTY_TAGS = "tags";
   @JsonProperty(JSON_PROPERTY_TAGS)
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/jaxrs-resteasy/default/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-resteasy/default/src/gen/java/org/openapitools/model/Pet.java
index 2b0dc308e13..b2c00a8a1ae 100644
--- a/samples/server/petstore/jaxrs-resteasy/default/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-resteasy/default/src/gen/java/org/openapitools/model/Pet.java
@@ -24,7 +24,7 @@ public class Pet   {
   private Category category;
   private String name;
   private List<String> photoUrls = new ArrayList<>();
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/jaxrs-resteasy/eap-java8/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-resteasy/eap-java8/src/gen/java/org/openapitools/model/Pet.java
index 0c7aab399ff..68027f2cfee 100644
--- a/samples/server/petstore/jaxrs-resteasy/eap-java8/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-resteasy/eap-java8/src/gen/java/org/openapitools/model/Pet.java
@@ -23,7 +23,7 @@ public class Pet   {
   private Category category;
   private String name;
   private List<String> photoUrls = new ArrayList<>();
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/jaxrs-resteasy/eap-joda/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-resteasy/eap-joda/src/gen/java/org/openapitools/model/Pet.java
index 0c7aab399ff..68027f2cfee 100644
--- a/samples/server/petstore/jaxrs-resteasy/eap-joda/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-resteasy/eap-joda/src/gen/java/org/openapitools/model/Pet.java
@@ -23,7 +23,7 @@ public class Pet   {
   private Category category;
   private String name;
   private List<String> photoUrls = new ArrayList<>();
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/jaxrs-resteasy/eap/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-resteasy/eap/src/gen/java/org/openapitools/model/Pet.java
index 0c7aab399ff..68027f2cfee 100644
--- a/samples/server/petstore/jaxrs-resteasy/eap/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-resteasy/eap/src/gen/java/org/openapitools/model/Pet.java
@@ -23,7 +23,7 @@ public class Pet   {
   private Category category;
   private String name;
   private List<String> photoUrls = new ArrayList<>();
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/jaxrs-resteasy/java8/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-resteasy/java8/src/gen/java/org/openapitools/model/Pet.java
index 2b0dc308e13..b2c00a8a1ae 100644
--- a/samples/server/petstore/jaxrs-resteasy/java8/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-resteasy/java8/src/gen/java/org/openapitools/model/Pet.java
@@ -24,7 +24,7 @@ public class Pet   {
   private Category category;
   private String name;
   private List<String> photoUrls = new ArrayList<>();
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/jaxrs-resteasy/joda/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-resteasy/joda/src/gen/java/org/openapitools/model/Pet.java
index 2b0dc308e13..b2c00a8a1ae 100644
--- a/samples/server/petstore/jaxrs-resteasy/joda/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-resteasy/joda/src/gen/java/org/openapitools/model/Pet.java
@@ -24,7 +24,7 @@ public class Pet   {
   private Category category;
   private String name;
   private List<String> photoUrls = new ArrayList<>();
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index 944817fcc42..544a79fe70c 100644
--- a/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -22,7 +22,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @JsonTypeName("ArrayOfArrayOfNumberOnly")
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly  implements Serializable {
-  private @Valid List<List<BigDecimal>> arrayArrayNumber;
+  private @Valid List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   /**
    **/
diff --git a/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
index 7bc098482de..83074c3b923 100644
--- a/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -22,7 +22,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @JsonTypeName("ArrayOfNumberOnly")
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly  implements Serializable {
-  private @Valid List<BigDecimal> arrayNumber;
+  private @Valid List<BigDecimal> arrayNumber = new ArrayList<>();
 
   /**
    **/
diff --git a/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/ArrayTest.java
index 6087ec02a9f..f58ed8ad766 100644
--- a/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/ArrayTest.java
@@ -22,9 +22,9 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @JsonTypeName("ArrayTest")
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest  implements Serializable {
-  private @Valid List<String> arrayOfString;
-  private @Valid List<List<Long>> arrayArrayOfInteger;
-  private @Valid List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private @Valid List<String> arrayOfString = new ArrayList<>();
+  private @Valid List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
+  private @Valid List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   /**
    **/
diff --git a/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/EnumArrays.java
index 54b24c766cc..08f67648afc 100644
--- a/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/EnumArrays.java
@@ -116,7 +116,7 @@ public class EnumArrays  implements Serializable {
     }
 }
 
-  private @Valid List<ArrayEnumEnum> arrayEnum;
+  private @Valid List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   /**
    **/
diff --git a/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
index 1e60309beab..e0353d057c1 100644
--- a/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
@@ -23,7 +23,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class FileSchemaTestClass  implements Serializable {
   private @Valid ModelFile _file;
-  private @Valid List<@Valid ModelFile> files;
+  private @Valid List<@Valid ModelFile> files = new ArrayList<>();
 
   /**
    **/
diff --git a/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/Pet.java
index 187182eff6a..4828f7fcc2e 100644
--- a/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/Pet.java
@@ -30,7 +30,7 @@ public class Pet  implements Serializable {
   private @Valid Category category;
   private @Valid String name;
   private @Valid Set<String> photoUrls = new LinkedHashSet<>();
-  private @Valid List<@Valid Tag> tags;
+  private @Valid List<@Valid Tag> tags = new ArrayList<>();
   public enum StatusEnum {
 
     AVAILABLE(String.valueOf("available")), PENDING(String.valueOf("pending")), SOLD(String.valueOf("sold"));
diff --git a/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/XmlItem.java
index 05edb3c86cb..b4e20d4ff6d 100644
--- a/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/jaxrs-spec-interface-response/src/gen/java/org/openapitools/model/XmlItem.java
@@ -26,31 +26,31 @@ public class XmlItem  implements Serializable {
   private @Valid BigDecimal attributeNumber;
   private @Valid Integer attributeInteger;
   private @Valid Boolean attributeBoolean;
-  private @Valid List<Integer> wrappedArray;
+  private @Valid List<Integer> wrappedArray = new ArrayList<>();
   private @Valid String nameString;
   private @Valid BigDecimal nameNumber;
   private @Valid Integer nameInteger;
   private @Valid Boolean nameBoolean;
-  private @Valid List<Integer> nameArray;
-  private @Valid List<Integer> nameWrappedArray;
+  private @Valid List<Integer> nameArray = new ArrayList<>();
+  private @Valid List<Integer> nameWrappedArray = new ArrayList<>();
   private @Valid String prefixString;
   private @Valid BigDecimal prefixNumber;
   private @Valid Integer prefixInteger;
   private @Valid Boolean prefixBoolean;
-  private @Valid List<Integer> prefixArray;
-  private @Valid List<Integer> prefixWrappedArray;
+  private @Valid List<Integer> prefixArray = new ArrayList<>();
+  private @Valid List<Integer> prefixWrappedArray = new ArrayList<>();
   private @Valid String namespaceString;
   private @Valid BigDecimal namespaceNumber;
   private @Valid Integer namespaceInteger;
   private @Valid Boolean namespaceBoolean;
-  private @Valid List<Integer> namespaceArray;
-  private @Valid List<Integer> namespaceWrappedArray;
+  private @Valid List<Integer> namespaceArray = new ArrayList<>();
+  private @Valid List<Integer> namespaceWrappedArray = new ArrayList<>();
   private @Valid String prefixNsString;
   private @Valid BigDecimal prefixNsNumber;
   private @Valid Integer prefixNsInteger;
   private @Valid Boolean prefixNsBoolean;
-  private @Valid List<Integer> prefixNsArray;
-  private @Valid List<Integer> prefixNsWrappedArray;
+  private @Valid List<Integer> prefixNsArray = new ArrayList<>();
+  private @Valid List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   /**
    **/
diff --git a/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index 944817fcc42..544a79fe70c 100644
--- a/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -22,7 +22,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @JsonTypeName("ArrayOfArrayOfNumberOnly")
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly  implements Serializable {
-  private @Valid List<List<BigDecimal>> arrayArrayNumber;
+  private @Valid List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   /**
    **/
diff --git a/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
index 7bc098482de..83074c3b923 100644
--- a/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -22,7 +22,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @JsonTypeName("ArrayOfNumberOnly")
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly  implements Serializable {
-  private @Valid List<BigDecimal> arrayNumber;
+  private @Valid List<BigDecimal> arrayNumber = new ArrayList<>();
 
   /**
    **/
diff --git a/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/ArrayTest.java
index 6087ec02a9f..f58ed8ad766 100644
--- a/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/ArrayTest.java
@@ -22,9 +22,9 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @JsonTypeName("ArrayTest")
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest  implements Serializable {
-  private @Valid List<String> arrayOfString;
-  private @Valid List<List<Long>> arrayArrayOfInteger;
-  private @Valid List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private @Valid List<String> arrayOfString = new ArrayList<>();
+  private @Valid List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
+  private @Valid List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   /**
    **/
diff --git a/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/EnumArrays.java
index 54b24c766cc..08f67648afc 100644
--- a/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/EnumArrays.java
@@ -116,7 +116,7 @@ public class EnumArrays  implements Serializable {
     }
 }
 
-  private @Valid List<ArrayEnumEnum> arrayEnum;
+  private @Valid List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   /**
    **/
diff --git a/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
index 1e60309beab..e0353d057c1 100644
--- a/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
@@ -23,7 +23,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class FileSchemaTestClass  implements Serializable {
   private @Valid ModelFile _file;
-  private @Valid List<@Valid ModelFile> files;
+  private @Valid List<@Valid ModelFile> files = new ArrayList<>();
 
   /**
    **/
diff --git a/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/Pet.java
index 187182eff6a..4828f7fcc2e 100644
--- a/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/Pet.java
@@ -30,7 +30,7 @@ public class Pet  implements Serializable {
   private @Valid Category category;
   private @Valid String name;
   private @Valid Set<String> photoUrls = new LinkedHashSet<>();
-  private @Valid List<@Valid Tag> tags;
+  private @Valid List<@Valid Tag> tags = new ArrayList<>();
   public enum StatusEnum {
 
     AVAILABLE(String.valueOf("available")), PENDING(String.valueOf("pending")), SOLD(String.valueOf("sold"));
diff --git a/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/XmlItem.java
index 05edb3c86cb..b4e20d4ff6d 100644
--- a/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/jaxrs-spec-interface/src/gen/java/org/openapitools/model/XmlItem.java
@@ -26,31 +26,31 @@ public class XmlItem  implements Serializable {
   private @Valid BigDecimal attributeNumber;
   private @Valid Integer attributeInteger;
   private @Valid Boolean attributeBoolean;
-  private @Valid List<Integer> wrappedArray;
+  private @Valid List<Integer> wrappedArray = new ArrayList<>();
   private @Valid String nameString;
   private @Valid BigDecimal nameNumber;
   private @Valid Integer nameInteger;
   private @Valid Boolean nameBoolean;
-  private @Valid List<Integer> nameArray;
-  private @Valid List<Integer> nameWrappedArray;
+  private @Valid List<Integer> nameArray = new ArrayList<>();
+  private @Valid List<Integer> nameWrappedArray = new ArrayList<>();
   private @Valid String prefixString;
   private @Valid BigDecimal prefixNumber;
   private @Valid Integer prefixInteger;
   private @Valid Boolean prefixBoolean;
-  private @Valid List<Integer> prefixArray;
-  private @Valid List<Integer> prefixWrappedArray;
+  private @Valid List<Integer> prefixArray = new ArrayList<>();
+  private @Valid List<Integer> prefixWrappedArray = new ArrayList<>();
   private @Valid String namespaceString;
   private @Valid BigDecimal namespaceNumber;
   private @Valid Integer namespaceInteger;
   private @Valid Boolean namespaceBoolean;
-  private @Valid List<Integer> namespaceArray;
-  private @Valid List<Integer> namespaceWrappedArray;
+  private @Valid List<Integer> namespaceArray = new ArrayList<>();
+  private @Valid List<Integer> namespaceWrappedArray = new ArrayList<>();
   private @Valid String prefixNsString;
   private @Valid BigDecimal prefixNsNumber;
   private @Valid Integer prefixNsInteger;
   private @Valid Boolean prefixNsBoolean;
-  private @Valid List<Integer> prefixNsArray;
-  private @Valid List<Integer> prefixNsWrappedArray;
+  private @Valid List<Integer> prefixNsArray = new ArrayList<>();
+  private @Valid List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   /**
    **/
diff --git a/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index ea7a70f6103..c1ca312074a 100644
--- a/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -22,7 +22,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @JsonTypeName("ArrayOfArrayOfNumberOnly")
 @jakarta.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly  implements Serializable {
-  private @Valid List<List<BigDecimal>> arrayArrayNumber;
+  private @Valid List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   protected ArrayOfArrayOfNumberOnly(ArrayOfArrayOfNumberOnlyBuilder<?, ?> b) {
     this.arrayArrayNumber = b.arrayArrayNumber;
@@ -124,7 +124,7 @@ public class ArrayOfArrayOfNumberOnly  implements Serializable {
   }
 
   public static abstract class ArrayOfArrayOfNumberOnlyBuilder<C extends ArrayOfArrayOfNumberOnly, B extends ArrayOfArrayOfNumberOnlyBuilder<C, B>>  {
-    private List<List<BigDecimal>> arrayArrayNumber;
+    private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
index 9024e5100e8..d59a6aa4541 100644
--- a/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -22,7 +22,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @JsonTypeName("ArrayOfNumberOnly")
 @jakarta.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly  implements Serializable {
-  private @Valid List<BigDecimal> arrayNumber;
+  private @Valid List<BigDecimal> arrayNumber = new ArrayList<>();
 
   protected ArrayOfNumberOnly(ArrayOfNumberOnlyBuilder<?, ?> b) {
     this.arrayNumber = b.arrayNumber;
@@ -124,7 +124,7 @@ public class ArrayOfNumberOnly  implements Serializable {
   }
 
   public static abstract class ArrayOfNumberOnlyBuilder<C extends ArrayOfNumberOnly, B extends ArrayOfNumberOnlyBuilder<C, B>>  {
-    private List<BigDecimal> arrayNumber;
+    private List<BigDecimal> arrayNumber = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/ArrayTest.java
index 45dfc2bc230..d76cd36445a 100644
--- a/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/ArrayTest.java
@@ -22,9 +22,9 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @JsonTypeName("ArrayTest")
 @jakarta.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest  implements Serializable {
-  private @Valid List<String> arrayOfString;
-  private @Valid List<List<Long>> arrayArrayOfInteger;
-  private @Valid List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private @Valid List<String> arrayOfString = new ArrayList<>();
+  private @Valid List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
+  private @Valid List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   protected ArrayTest(ArrayTestBuilder<?, ?> b) {
     this.arrayOfString = b.arrayOfString;
@@ -202,9 +202,9 @@ public class ArrayTest  implements Serializable {
   }
 
   public static abstract class ArrayTestBuilder<C extends ArrayTest, B extends ArrayTestBuilder<C, B>>  {
-    private List<String> arrayOfString;
-    private List<List<Long>> arrayArrayOfInteger;
-    private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+    private List<String> arrayOfString = new ArrayList<>();
+    private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
+    private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/EnumArrays.java
index 86946cb3258..c55d1446e11 100644
--- a/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/EnumArrays.java
@@ -116,7 +116,7 @@ public class EnumArrays  implements Serializable {
     }
 }
 
-  private @Valid List<ArrayEnumEnum> arrayEnum;
+  private @Valid List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   protected EnumArrays(EnumArraysBuilder<?, ?> b) {
     this.justSymbol = b.justSymbol;
@@ -241,7 +241,7 @@ public class EnumArrays  implements Serializable {
 
   public static abstract class EnumArraysBuilder<C extends EnumArrays, B extends EnumArraysBuilder<C, B>>  {
     private JustSymbolEnum justSymbol;
-    private List<ArrayEnumEnum> arrayEnum;
+    private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
index 537c23ac83f..8ab54ca8c09 100644
--- a/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
@@ -23,7 +23,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @jakarta.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class FileSchemaTestClass  implements Serializable {
   private @Valid ModelFile _file;
-  private @Valid List<@Valid ModelFile> files;
+  private @Valid List<@Valid ModelFile> files = new ArrayList<>();
 
   protected FileSchemaTestClass(FileSchemaTestClassBuilder<?, ?> b) {
     this._file = b._file;
@@ -148,7 +148,7 @@ public class FileSchemaTestClass  implements Serializable {
 
   public static abstract class FileSchemaTestClassBuilder<C extends FileSchemaTestClass, B extends FileSchemaTestClassBuilder<C, B>>  {
     private ModelFile _file;
-    private List<@Valid ModelFile> files;
+    private List<@Valid ModelFile> files = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/Pet.java
index 83cd0726547..23fe64a6cd9 100644
--- a/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/Pet.java
@@ -30,7 +30,7 @@ public class Pet  implements Serializable {
   private @Valid Category category;
   private @Valid String name;
   private @Valid Set<String> photoUrls = new LinkedHashSet<>();
-  private @Valid List<@Valid Tag> tags;
+  private @Valid List<@Valid Tag> tags = new ArrayList<>();
   public enum StatusEnum {
 
     AVAILABLE(String.valueOf("available")), PENDING(String.valueOf("pending")), SOLD(String.valueOf("sold"));
@@ -314,7 +314,7 @@ public class Pet  implements Serializable {
     private Category category;
     private String name;
     private Set<String> photoUrls = new LinkedHashSet<>();
-    private List<@Valid Tag> tags;
+    private List<@Valid Tag> tags = new ArrayList<>();
     private StatusEnum status;
     protected abstract B self();
 
diff --git a/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/XmlItem.java
index 35dadc911a3..f3745ff6378 100644
--- a/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/jaxrs-spec-jakarta/src/gen/java/org/openapitools/model/XmlItem.java
@@ -26,31 +26,31 @@ public class XmlItem  implements Serializable {
   private @Valid BigDecimal attributeNumber;
   private @Valid Integer attributeInteger;
   private @Valid Boolean attributeBoolean;
-  private @Valid List<Integer> wrappedArray;
+  private @Valid List<Integer> wrappedArray = new ArrayList<>();
   private @Valid String nameString;
   private @Valid BigDecimal nameNumber;
   private @Valid Integer nameInteger;
   private @Valid Boolean nameBoolean;
-  private @Valid List<Integer> nameArray;
-  private @Valid List<Integer> nameWrappedArray;
+  private @Valid List<Integer> nameArray = new ArrayList<>();
+  private @Valid List<Integer> nameWrappedArray = new ArrayList<>();
   private @Valid String prefixString;
   private @Valid BigDecimal prefixNumber;
   private @Valid Integer prefixInteger;
   private @Valid Boolean prefixBoolean;
-  private @Valid List<Integer> prefixArray;
-  private @Valid List<Integer> prefixWrappedArray;
+  private @Valid List<Integer> prefixArray = new ArrayList<>();
+  private @Valid List<Integer> prefixWrappedArray = new ArrayList<>();
   private @Valid String namespaceString;
   private @Valid BigDecimal namespaceNumber;
   private @Valid Integer namespaceInteger;
   private @Valid Boolean namespaceBoolean;
-  private @Valid List<Integer> namespaceArray;
-  private @Valid List<Integer> namespaceWrappedArray;
+  private @Valid List<Integer> namespaceArray = new ArrayList<>();
+  private @Valid List<Integer> namespaceWrappedArray = new ArrayList<>();
   private @Valid String prefixNsString;
   private @Valid BigDecimal prefixNsNumber;
   private @Valid Integer prefixNsInteger;
   private @Valid Boolean prefixNsBoolean;
-  private @Valid List<Integer> prefixNsArray;
-  private @Valid List<Integer> prefixNsWrappedArray;
+  private @Valid List<Integer> prefixNsArray = new ArrayList<>();
+  private @Valid List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   protected XmlItem(XmlItemBuilder<?, ?> b) {
     this.attributeString = b.attributeString;
@@ -900,31 +900,31 @@ public class XmlItem  implements Serializable {
     private BigDecimal attributeNumber;
     private Integer attributeInteger;
     private Boolean attributeBoolean;
-    private List<Integer> wrappedArray;
+    private List<Integer> wrappedArray = new ArrayList<>();
     private String nameString;
     private BigDecimal nameNumber;
     private Integer nameInteger;
     private Boolean nameBoolean;
-    private List<Integer> nameArray;
-    private List<Integer> nameWrappedArray;
+    private List<Integer> nameArray = new ArrayList<>();
+    private List<Integer> nameWrappedArray = new ArrayList<>();
     private String prefixString;
     private BigDecimal prefixNumber;
     private Integer prefixInteger;
     private Boolean prefixBoolean;
-    private List<Integer> prefixArray;
-    private List<Integer> prefixWrappedArray;
+    private List<Integer> prefixArray = new ArrayList<>();
+    private List<Integer> prefixWrappedArray = new ArrayList<>();
     private String namespaceString;
     private BigDecimal namespaceNumber;
     private Integer namespaceInteger;
     private Boolean namespaceBoolean;
-    private List<Integer> namespaceArray;
-    private List<Integer> namespaceWrappedArray;
+    private List<Integer> namespaceArray = new ArrayList<>();
+    private List<Integer> namespaceWrappedArray = new ArrayList<>();
     private String prefixNsString;
     private BigDecimal prefixNsNumber;
     private Integer prefixNsInteger;
     private Boolean prefixNsBoolean;
-    private List<Integer> prefixNsArray;
-    private List<Integer> prefixNsWrappedArray;
+    private List<Integer> prefixNsArray = new ArrayList<>();
+    private List<Integer> prefixNsWrappedArray = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index ef59cfafd7d..1c28ed8e719 100644
--- a/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -20,7 +20,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @JsonTypeName("ArrayOfArrayOfNumberOnly")
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly  implements Serializable {
-  private @Valid List<List<BigDecimal>> arrayArrayNumber;
+  private @Valid List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   protected ArrayOfArrayOfNumberOnly(ArrayOfArrayOfNumberOnlyBuilder<?, ?> b) {
     this.arrayArrayNumber = b.arrayArrayNumber;
@@ -122,7 +122,7 @@ public class ArrayOfArrayOfNumberOnly  implements Serializable {
   }
 
   public static abstract class ArrayOfArrayOfNumberOnlyBuilder<C extends ArrayOfArrayOfNumberOnly, B extends ArrayOfArrayOfNumberOnlyBuilder<C, B>>  {
-    private List<List<BigDecimal>> arrayArrayNumber;
+    private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
index 672e2ad53b8..55be283941d 100644
--- a/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -20,7 +20,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @JsonTypeName("ArrayOfNumberOnly")
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly  implements Serializable {
-  private @Valid List<BigDecimal> arrayNumber;
+  private @Valid List<BigDecimal> arrayNumber = new ArrayList<>();
 
   protected ArrayOfNumberOnly(ArrayOfNumberOnlyBuilder<?, ?> b) {
     this.arrayNumber = b.arrayNumber;
@@ -122,7 +122,7 @@ public class ArrayOfNumberOnly  implements Serializable {
   }
 
   public static abstract class ArrayOfNumberOnlyBuilder<C extends ArrayOfNumberOnly, B extends ArrayOfNumberOnlyBuilder<C, B>>  {
-    private List<BigDecimal> arrayNumber;
+    private List<BigDecimal> arrayNumber = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/ArrayTest.java
index e9f7715b0ae..8e5a1529327 100644
--- a/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/ArrayTest.java
@@ -20,9 +20,9 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @JsonTypeName("ArrayTest")
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest  implements Serializable {
-  private @Valid List<String> arrayOfString;
-  private @Valid List<List<Long>> arrayArrayOfInteger;
-  private @Valid List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private @Valid List<String> arrayOfString = new ArrayList<>();
+  private @Valid List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
+  private @Valid List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   protected ArrayTest(ArrayTestBuilder<?, ?> b) {
     this.arrayOfString = b.arrayOfString;
@@ -200,9 +200,9 @@ public class ArrayTest  implements Serializable {
   }
 
   public static abstract class ArrayTestBuilder<C extends ArrayTest, B extends ArrayTestBuilder<C, B>>  {
-    private List<String> arrayOfString;
-    private List<List<Long>> arrayArrayOfInteger;
-    private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+    private List<String> arrayOfString = new ArrayList<>();
+    private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
+    private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/EnumArrays.java
index 9736bf93a2d..954bcf2ef58 100644
--- a/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/EnumArrays.java
@@ -114,7 +114,7 @@ public class EnumArrays  implements Serializable {
     }
 }
 
-  private @Valid List<ArrayEnumEnum> arrayEnum;
+  private @Valid List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   protected EnumArrays(EnumArraysBuilder<?, ?> b) {
     this.justSymbol = b.justSymbol;
@@ -239,7 +239,7 @@ public class EnumArrays  implements Serializable {
 
   public static abstract class EnumArraysBuilder<C extends EnumArrays, B extends EnumArraysBuilder<C, B>>  {
     private JustSymbolEnum justSymbol;
-    private List<ArrayEnumEnum> arrayEnum;
+    private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
index 91a345202cc..2ac3016d7f0 100644
--- a/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
@@ -21,7 +21,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class FileSchemaTestClass  implements Serializable {
   private @Valid ModelFile _file;
-  private @Valid List<@Valid ModelFile> files;
+  private @Valid List<@Valid ModelFile> files = new ArrayList<>();
 
   protected FileSchemaTestClass(FileSchemaTestClassBuilder<?, ?> b) {
     this._file = b._file;
@@ -146,7 +146,7 @@ public class FileSchemaTestClass  implements Serializable {
 
   public static abstract class FileSchemaTestClassBuilder<C extends FileSchemaTestClass, B extends FileSchemaTestClassBuilder<C, B>>  {
     private ModelFile _file;
-    private List<@Valid ModelFile> files;
+    private List<@Valid ModelFile> files = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/Pet.java
index e222101e1d4..cda86f596fa 100644
--- a/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/Pet.java
@@ -28,7 +28,7 @@ public class Pet  implements Serializable {
   private @Valid Category category;
   private @Valid String name;
   private @Valid Set<String> photoUrls = new LinkedHashSet<>();
-  private @Valid List<@Valid Tag> tags;
+  private @Valid List<@Valid Tag> tags = new ArrayList<>();
   public enum StatusEnum {
 
     AVAILABLE(String.valueOf("available")), PENDING(String.valueOf("pending")), SOLD(String.valueOf("sold"));
@@ -312,7 +312,7 @@ public class Pet  implements Serializable {
     private Category category;
     private String name;
     private Set<String> photoUrls = new LinkedHashSet<>();
-    private List<@Valid Tag> tags;
+    private List<@Valid Tag> tags = new ArrayList<>();
     private StatusEnum status;
     protected abstract B self();
 
diff --git a/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/XmlItem.java
index 9287da4a6f7..523d7c14142 100644
--- a/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/jaxrs-spec-microprofile-openapi-annotations/src/gen/java/org/openapitools/model/XmlItem.java
@@ -24,31 +24,31 @@ public class XmlItem  implements Serializable {
   private @Valid BigDecimal attributeNumber;
   private @Valid Integer attributeInteger;
   private @Valid Boolean attributeBoolean;
-  private @Valid List<Integer> wrappedArray;
+  private @Valid List<Integer> wrappedArray = new ArrayList<>();
   private @Valid String nameString;
   private @Valid BigDecimal nameNumber;
   private @Valid Integer nameInteger;
   private @Valid Boolean nameBoolean;
-  private @Valid List<Integer> nameArray;
-  private @Valid List<Integer> nameWrappedArray;
+  private @Valid List<Integer> nameArray = new ArrayList<>();
+  private @Valid List<Integer> nameWrappedArray = new ArrayList<>();
   private @Valid String prefixString;
   private @Valid BigDecimal prefixNumber;
   private @Valid Integer prefixInteger;
   private @Valid Boolean prefixBoolean;
-  private @Valid List<Integer> prefixArray;
-  private @Valid List<Integer> prefixWrappedArray;
+  private @Valid List<Integer> prefixArray = new ArrayList<>();
+  private @Valid List<Integer> prefixWrappedArray = new ArrayList<>();
   private @Valid String namespaceString;
   private @Valid BigDecimal namespaceNumber;
   private @Valid Integer namespaceInteger;
   private @Valid Boolean namespaceBoolean;
-  private @Valid List<Integer> namespaceArray;
-  private @Valid List<Integer> namespaceWrappedArray;
+  private @Valid List<Integer> namespaceArray = new ArrayList<>();
+  private @Valid List<Integer> namespaceWrappedArray = new ArrayList<>();
   private @Valid String prefixNsString;
   private @Valid BigDecimal prefixNsNumber;
   private @Valid Integer prefixNsInteger;
   private @Valid Boolean prefixNsBoolean;
-  private @Valid List<Integer> prefixNsArray;
-  private @Valid List<Integer> prefixNsWrappedArray;
+  private @Valid List<Integer> prefixNsArray = new ArrayList<>();
+  private @Valid List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   protected XmlItem(XmlItemBuilder<?, ?> b) {
     this.attributeString = b.attributeString;
@@ -898,31 +898,31 @@ public class XmlItem  implements Serializable {
     private BigDecimal attributeNumber;
     private Integer attributeInteger;
     private Boolean attributeBoolean;
-    private List<Integer> wrappedArray;
+    private List<Integer> wrappedArray = new ArrayList<>();
     private String nameString;
     private BigDecimal nameNumber;
     private Integer nameInteger;
     private Boolean nameBoolean;
-    private List<Integer> nameArray;
-    private List<Integer> nameWrappedArray;
+    private List<Integer> nameArray = new ArrayList<>();
+    private List<Integer> nameWrappedArray = new ArrayList<>();
     private String prefixString;
     private BigDecimal prefixNumber;
     private Integer prefixInteger;
     private Boolean prefixBoolean;
-    private List<Integer> prefixArray;
-    private List<Integer> prefixWrappedArray;
+    private List<Integer> prefixArray = new ArrayList<>();
+    private List<Integer> prefixWrappedArray = new ArrayList<>();
     private String namespaceString;
     private BigDecimal namespaceNumber;
     private Integer namespaceInteger;
     private Boolean namespaceBoolean;
-    private List<Integer> namespaceArray;
-    private List<Integer> namespaceWrappedArray;
+    private List<Integer> namespaceArray = new ArrayList<>();
+    private List<Integer> namespaceWrappedArray = new ArrayList<>();
     private String prefixNsString;
     private BigDecimal prefixNsNumber;
     private Integer prefixNsInteger;
     private Boolean prefixNsBoolean;
-    private List<Integer> prefixNsArray;
-    private List<Integer> prefixNsWrappedArray;
+    private List<Integer> prefixNsArray = new ArrayList<>();
+    private List<Integer> prefixNsWrappedArray = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index a3fbd1c93ac..13401f3d90c 100644
--- a/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -22,7 +22,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @JsonTypeName("ArrayOfArrayOfNumberOnly")
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfArrayOfNumberOnly  implements Serializable {
-  private @Valid List<List<BigDecimal>> arrayArrayNumber;
+  private @Valid List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   protected ArrayOfArrayOfNumberOnly(ArrayOfArrayOfNumberOnlyBuilder<?, ?> b) {
     this.arrayArrayNumber = b.arrayArrayNumber;
@@ -124,7 +124,7 @@ public class ArrayOfArrayOfNumberOnly  implements Serializable {
   }
 
   public static abstract class ArrayOfArrayOfNumberOnlyBuilder<C extends ArrayOfArrayOfNumberOnly, B extends ArrayOfArrayOfNumberOnlyBuilder<C, B>>  {
-    private List<List<BigDecimal>> arrayArrayNumber;
+    private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
index e734770b002..ed92ac73c24 100644
--- a/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -22,7 +22,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @JsonTypeName("ArrayOfNumberOnly")
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayOfNumberOnly  implements Serializable {
-  private @Valid List<BigDecimal> arrayNumber;
+  private @Valid List<BigDecimal> arrayNumber = new ArrayList<>();
 
   protected ArrayOfNumberOnly(ArrayOfNumberOnlyBuilder<?, ?> b) {
     this.arrayNumber = b.arrayNumber;
@@ -124,7 +124,7 @@ public class ArrayOfNumberOnly  implements Serializable {
   }
 
   public static abstract class ArrayOfNumberOnlyBuilder<C extends ArrayOfNumberOnly, B extends ArrayOfNumberOnlyBuilder<C, B>>  {
-    private List<BigDecimal> arrayNumber;
+    private List<BigDecimal> arrayNumber = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/ArrayTest.java
index c6cb875034a..7790ae114e3 100644
--- a/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/ArrayTest.java
@@ -22,9 +22,9 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @JsonTypeName("ArrayTest")
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class ArrayTest  implements Serializable {
-  private @Valid List<String> arrayOfString;
-  private @Valid List<List<Long>> arrayArrayOfInteger;
-  private @Valid List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private @Valid List<String> arrayOfString = new ArrayList<>();
+  private @Valid List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
+  private @Valid List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   protected ArrayTest(ArrayTestBuilder<?, ?> b) {
     this.arrayOfString = b.arrayOfString;
@@ -202,9 +202,9 @@ public class ArrayTest  implements Serializable {
   }
 
   public static abstract class ArrayTestBuilder<C extends ArrayTest, B extends ArrayTestBuilder<C, B>>  {
-    private List<String> arrayOfString;
-    private List<List<Long>> arrayArrayOfInteger;
-    private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+    private List<String> arrayOfString = new ArrayList<>();
+    private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
+    private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/EnumArrays.java
index bdd40eb6994..ab87f4c939a 100644
--- a/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/EnumArrays.java
@@ -116,7 +116,7 @@ public class EnumArrays  implements Serializable {
     }
 }
 
-  private @Valid List<ArrayEnumEnum> arrayEnum;
+  private @Valid List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   protected EnumArrays(EnumArraysBuilder<?, ?> b) {
     this.justSymbol = b.justSymbol;
@@ -241,7 +241,7 @@ public class EnumArrays  implements Serializable {
 
   public static abstract class EnumArraysBuilder<C extends EnumArrays, B extends EnumArraysBuilder<C, B>>  {
     private JustSymbolEnum justSymbol;
-    private List<ArrayEnumEnum> arrayEnum;
+    private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
index a3b262f817b..5a67940ea3d 100644
--- a/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
@@ -23,7 +23,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJAXRSSpecServerCodegen", comments = "Generator version: 7.5.0-SNAPSHOT")
 public class FileSchemaTestClass  implements Serializable {
   private @Valid ModelFile _file;
-  private @Valid List<@Valid ModelFile> files;
+  private @Valid List<@Valid ModelFile> files = new ArrayList<>();
 
   protected FileSchemaTestClass(FileSchemaTestClassBuilder<?, ?> b) {
     this._file = b._file;
@@ -148,7 +148,7 @@ public class FileSchemaTestClass  implements Serializable {
 
   public static abstract class FileSchemaTestClassBuilder<C extends FileSchemaTestClass, B extends FileSchemaTestClassBuilder<C, B>>  {
     private ModelFile _file;
-    private List<@Valid ModelFile> files;
+    private List<@Valid ModelFile> files = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/Pet.java
index dc796440441..2fd4a45f6e7 100644
--- a/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/Pet.java
@@ -30,7 +30,7 @@ public class Pet  implements Serializable {
   private @Valid Category category;
   private @Valid String name;
   private @Valid Set<String> photoUrls = new LinkedHashSet<>();
-  private @Valid List<@Valid Tag> tags;
+  private @Valid List<@Valid Tag> tags = new ArrayList<>();
   public enum StatusEnum {
 
     AVAILABLE(String.valueOf("available")), PENDING(String.valueOf("pending")), SOLD(String.valueOf("sold"));
@@ -314,7 +314,7 @@ public class Pet  implements Serializable {
     private Category category;
     private String name;
     private Set<String> photoUrls = new LinkedHashSet<>();
-    private List<@Valid Tag> tags;
+    private List<@Valid Tag> tags = new ArrayList<>();
     private StatusEnum status;
     protected abstract B self();
 
diff --git a/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/XmlItem.java
index b63f4c64bec..0558488f93b 100644
--- a/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/jaxrs-spec/src/gen/java/org/openapitools/model/XmlItem.java
@@ -26,31 +26,31 @@ public class XmlItem  implements Serializable {
   private @Valid BigDecimal attributeNumber;
   private @Valid Integer attributeInteger;
   private @Valid Boolean attributeBoolean;
-  private @Valid List<Integer> wrappedArray;
+  private @Valid List<Integer> wrappedArray = new ArrayList<>();
   private @Valid String nameString;
   private @Valid BigDecimal nameNumber;
   private @Valid Integer nameInteger;
   private @Valid Boolean nameBoolean;
-  private @Valid List<Integer> nameArray;
-  private @Valid List<Integer> nameWrappedArray;
+  private @Valid List<Integer> nameArray = new ArrayList<>();
+  private @Valid List<Integer> nameWrappedArray = new ArrayList<>();
   private @Valid String prefixString;
   private @Valid BigDecimal prefixNumber;
   private @Valid Integer prefixInteger;
   private @Valid Boolean prefixBoolean;
-  private @Valid List<Integer> prefixArray;
-  private @Valid List<Integer> prefixWrappedArray;
+  private @Valid List<Integer> prefixArray = new ArrayList<>();
+  private @Valid List<Integer> prefixWrappedArray = new ArrayList<>();
   private @Valid String namespaceString;
   private @Valid BigDecimal namespaceNumber;
   private @Valid Integer namespaceInteger;
   private @Valid Boolean namespaceBoolean;
-  private @Valid List<Integer> namespaceArray;
-  private @Valid List<Integer> namespaceWrappedArray;
+  private @Valid List<Integer> namespaceArray = new ArrayList<>();
+  private @Valid List<Integer> namespaceWrappedArray = new ArrayList<>();
   private @Valid String prefixNsString;
   private @Valid BigDecimal prefixNsNumber;
   private @Valid Integer prefixNsInteger;
   private @Valid Boolean prefixNsBoolean;
-  private @Valid List<Integer> prefixNsArray;
-  private @Valid List<Integer> prefixNsWrappedArray;
+  private @Valid List<Integer> prefixNsArray = new ArrayList<>();
+  private @Valid List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   protected XmlItem(XmlItemBuilder<?, ?> b) {
     this.attributeString = b.attributeString;
@@ -900,31 +900,31 @@ public class XmlItem  implements Serializable {
     private BigDecimal attributeNumber;
     private Integer attributeInteger;
     private Boolean attributeBoolean;
-    private List<Integer> wrappedArray;
+    private List<Integer> wrappedArray = new ArrayList<>();
     private String nameString;
     private BigDecimal nameNumber;
     private Integer nameInteger;
     private Boolean nameBoolean;
-    private List<Integer> nameArray;
-    private List<Integer> nameWrappedArray;
+    private List<Integer> nameArray = new ArrayList<>();
+    private List<Integer> nameWrappedArray = new ArrayList<>();
     private String prefixString;
     private BigDecimal prefixNumber;
     private Integer prefixInteger;
     private Boolean prefixBoolean;
-    private List<Integer> prefixArray;
-    private List<Integer> prefixWrappedArray;
+    private List<Integer> prefixArray = new ArrayList<>();
+    private List<Integer> prefixWrappedArray = new ArrayList<>();
     private String namespaceString;
     private BigDecimal namespaceNumber;
     private Integer namespaceInteger;
     private Boolean namespaceBoolean;
-    private List<Integer> namespaceArray;
-    private List<Integer> namespaceWrappedArray;
+    private List<Integer> namespaceArray = new ArrayList<>();
+    private List<Integer> namespaceWrappedArray = new ArrayList<>();
     private String prefixNsString;
     private BigDecimal prefixNsNumber;
     private Integer prefixNsInteger;
     private Boolean prefixNsBoolean;
-    private List<Integer> prefixNsArray;
-    private List<Integer> prefixNsWrappedArray;
+    private List<Integer> prefixNsArray = new ArrayList<>();
+    private List<Integer> prefixNsWrappedArray = new ArrayList<>();
     protected abstract B self();
 
     public abstract C build();
diff --git a/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index 7e1a747d87e..58d71a089b5 100644
--- a/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import javax.validation.Valid;
 public class ArrayOfArrayOfNumberOnly   {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
   @JsonProperty(JSON_PROPERTY_ARRAY_ARRAY_NUMBER)
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
index fccb8d855a3..08d8883200f 100644
--- a/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import javax.validation.Valid;
 public class ArrayOfNumberOnly   {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
   @JsonProperty(JSON_PROPERTY_ARRAY_NUMBER)
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/ArrayTest.java
index 98b05ead441..db51df02256 100644
--- a/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/ArrayTest.java
@@ -38,15 +38,15 @@ import javax.validation.Valid;
 public class ArrayTest   {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
   @JsonProperty(JSON_PROPERTY_ARRAY_OF_STRING)
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
   @JsonProperty(JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER)
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
   @JsonProperty(JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL)
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/EnumArrays.java
index 23e0cafa0e2..90d11edf7e1 100644
--- a/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/EnumArrays.java
@@ -103,7 +103,7 @@ public class EnumArrays   {
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
   @JsonProperty(JSON_PROPERTY_ARRAY_ENUM)
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
index 4de852677f2..d88b0af4857 100644
--- a/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
@@ -41,7 +41,7 @@ public class FileSchemaTestClass   {
 
   public static final String JSON_PROPERTY_FILES = "files";
   @JsonProperty(JSON_PROPERTY_FILES)
-  private List<@Valid ModelFile> files;
+  private List<@Valid ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass _file(ModelFile _file) {
     this._file = _file;
diff --git a/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/Pet.java
index dc10d3ad53b..116f53a76a1 100644
--- a/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/Pet.java
@@ -62,7 +62,7 @@ public class Pet   {
 
   public static final String JSON_PROPERTY_TAGS = "tags";
   @JsonProperty(JSON_PROPERTY_TAGS)
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/XmlItem.java
index 2bc554ba6ea..5d478148e2b 100644
--- a/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/jaxrs/jersey2-useTags/src/gen/java/org/openapitools/model/XmlItem.java
@@ -80,7 +80,7 @@ public class XmlItem   {
 
   public static final String JSON_PROPERTY_WRAPPED_ARRAY = "wrapped_array";
   @JsonProperty(JSON_PROPERTY_WRAPPED_ARRAY)
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_STRING = "name_string";
   @JsonProperty(JSON_PROPERTY_NAME_STRING)
@@ -100,11 +100,11 @@ public class XmlItem   {
 
   public static final String JSON_PROPERTY_NAME_ARRAY = "name_array";
   @JsonProperty(JSON_PROPERTY_NAME_ARRAY)
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_WRAPPED_ARRAY = "name_wrapped_array";
   @JsonProperty(JSON_PROPERTY_NAME_WRAPPED_ARRAY)
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_STRING = "prefix_string";
   @JsonProperty(JSON_PROPERTY_PREFIX_STRING)
@@ -124,11 +124,11 @@ public class XmlItem   {
 
   public static final String JSON_PROPERTY_PREFIX_ARRAY = "prefix_array";
   @JsonProperty(JSON_PROPERTY_PREFIX_ARRAY)
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
   @JsonProperty(JSON_PROPERTY_PREFIX_WRAPPED_ARRAY)
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_STRING = "namespace_string";
   @JsonProperty(JSON_PROPERTY_NAMESPACE_STRING)
@@ -148,11 +148,11 @@ public class XmlItem   {
 
   public static final String JSON_PROPERTY_NAMESPACE_ARRAY = "namespace_array";
   @JsonProperty(JSON_PROPERTY_NAMESPACE_ARRAY)
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
   @JsonProperty(JSON_PROPERTY_NAMESPACE_WRAPPED_ARRAY)
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_STRING = "prefix_ns_string";
   @JsonProperty(JSON_PROPERTY_PREFIX_NS_STRING)
@@ -172,11 +172,11 @@ public class XmlItem   {
 
   public static final String JSON_PROPERTY_PREFIX_NS_ARRAY = "prefix_ns_array";
   @JsonProperty(JSON_PROPERTY_PREFIX_NS_ARRAY)
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
   @JsonProperty(JSON_PROPERTY_PREFIX_NS_WRAPPED_ARRAY)
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index 7e1a747d87e..58d71a089b5 100644
--- a/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import javax.validation.Valid;
 public class ArrayOfArrayOfNumberOnly   {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
   @JsonProperty(JSON_PROPERTY_ARRAY_ARRAY_NUMBER)
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
index fccb8d855a3..08d8883200f 100644
--- a/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -36,7 +36,7 @@ import javax.validation.Valid;
 public class ArrayOfNumberOnly   {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
   @JsonProperty(JSON_PROPERTY_ARRAY_NUMBER)
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/ArrayTest.java
index 98b05ead441..db51df02256 100644
--- a/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/ArrayTest.java
@@ -38,15 +38,15 @@ import javax.validation.Valid;
 public class ArrayTest   {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
   @JsonProperty(JSON_PROPERTY_ARRAY_OF_STRING)
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
   @JsonProperty(JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER)
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
   @JsonProperty(JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL)
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/EnumArrays.java
index 23e0cafa0e2..90d11edf7e1 100644
--- a/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/EnumArrays.java
@@ -103,7 +103,7 @@ public class EnumArrays   {
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
   @JsonProperty(JSON_PROPERTY_ARRAY_ENUM)
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
index 4de852677f2..d88b0af4857 100644
--- a/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
@@ -41,7 +41,7 @@ public class FileSchemaTestClass   {
 
   public static final String JSON_PROPERTY_FILES = "files";
   @JsonProperty(JSON_PROPERTY_FILES)
-  private List<@Valid ModelFile> files;
+  private List<@Valid ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass _file(ModelFile _file) {
     this._file = _file;
diff --git a/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/Pet.java
index dc10d3ad53b..116f53a76a1 100644
--- a/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/Pet.java
@@ -62,7 +62,7 @@ public class Pet   {
 
   public static final String JSON_PROPERTY_TAGS = "tags";
   @JsonProperty(JSON_PROPERTY_TAGS)
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/XmlItem.java
index 2bc554ba6ea..5d478148e2b 100644
--- a/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/jaxrs/jersey2/src/gen/java/org/openapitools/model/XmlItem.java
@@ -80,7 +80,7 @@ public class XmlItem   {
 
   public static final String JSON_PROPERTY_WRAPPED_ARRAY = "wrapped_array";
   @JsonProperty(JSON_PROPERTY_WRAPPED_ARRAY)
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_STRING = "name_string";
   @JsonProperty(JSON_PROPERTY_NAME_STRING)
@@ -100,11 +100,11 @@ public class XmlItem   {
 
   public static final String JSON_PROPERTY_NAME_ARRAY = "name_array";
   @JsonProperty(JSON_PROPERTY_NAME_ARRAY)
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAME_WRAPPED_ARRAY = "name_wrapped_array";
   @JsonProperty(JSON_PROPERTY_NAME_WRAPPED_ARRAY)
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_STRING = "prefix_string";
   @JsonProperty(JSON_PROPERTY_PREFIX_STRING)
@@ -124,11 +124,11 @@ public class XmlItem   {
 
   public static final String JSON_PROPERTY_PREFIX_ARRAY = "prefix_array";
   @JsonProperty(JSON_PROPERTY_PREFIX_ARRAY)
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_WRAPPED_ARRAY = "prefix_wrapped_array";
   @JsonProperty(JSON_PROPERTY_PREFIX_WRAPPED_ARRAY)
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_STRING = "namespace_string";
   @JsonProperty(JSON_PROPERTY_NAMESPACE_STRING)
@@ -148,11 +148,11 @@ public class XmlItem   {
 
   public static final String JSON_PROPERTY_NAMESPACE_ARRAY = "namespace_array";
   @JsonProperty(JSON_PROPERTY_NAMESPACE_ARRAY)
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_NAMESPACE_WRAPPED_ARRAY = "namespace_wrapped_array";
   @JsonProperty(JSON_PROPERTY_NAMESPACE_WRAPPED_ARRAY)
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_STRING = "prefix_ns_string";
   @JsonProperty(JSON_PROPERTY_PREFIX_NS_STRING)
@@ -172,11 +172,11 @@ public class XmlItem   {
 
   public static final String JSON_PROPERTY_PREFIX_NS_ARRAY = "prefix_ns_array";
   @JsonProperty(JSON_PROPERTY_PREFIX_NS_ARRAY)
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   public static final String JSON_PROPERTY_PREFIX_NS_WRAPPED_ARRAY = "prefix_ns_wrapped_array";
   @JsonProperty(JSON_PROPERTY_PREFIX_NS_WRAPPED_ARRAY)
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index fa0e462d4b3..ff34d45fb6a 100644
--- a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -35,7 +35,7 @@ import jakarta.validation.Valid;
 public class ArrayOfArrayOfNumberOnly   {
   public static final String JSON_PROPERTY_ARRAY_ARRAY_NUMBER = "ArrayArrayNumber";
   @JsonProperty(JSON_PROPERTY_ARRAY_ARRAY_NUMBER)
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
index b3cdbc2e615..7ad7a117e10 100644
--- a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -35,7 +35,7 @@ import jakarta.validation.Valid;
 public class ArrayOfNumberOnly   {
   public static final String JSON_PROPERTY_ARRAY_NUMBER = "ArrayNumber";
   @JsonProperty(JSON_PROPERTY_ARRAY_NUMBER)
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ArrayTest.java
index 1f6cc78254d..224f399026c 100644
--- a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ArrayTest.java
@@ -37,15 +37,15 @@ import jakarta.validation.Valid;
 public class ArrayTest   {
   public static final String JSON_PROPERTY_ARRAY_OF_STRING = "array_of_string";
   @JsonProperty(JSON_PROPERTY_ARRAY_OF_STRING)
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER = "array_array_of_integer";
   @JsonProperty(JSON_PROPERTY_ARRAY_ARRAY_OF_INTEGER)
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   public static final String JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL = "array_array_of_model";
   @JsonProperty(JSON_PROPERTY_ARRAY_ARRAY_OF_MODEL)
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/EnumArrays.java
index 44bc48e9a80..6ceb0a8a8ad 100644
--- a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/EnumArrays.java
@@ -102,7 +102,7 @@ public class EnumArrays   {
 
   public static final String JSON_PROPERTY_ARRAY_ENUM = "array_enum";
   @JsonProperty(JSON_PROPERTY_ARRAY_ENUM)
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
index 784ab2a420f..0b5528efa3e 100644
--- a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/FileSchemaTestClass.java
@@ -40,7 +40,7 @@ public class FileSchemaTestClass   {
 
   public static final String JSON_PROPERTY_FILES = "files";
   @JsonProperty(JSON_PROPERTY_FILES)
-  private List<@Valid ModelFile> files;
+  private List<@Valid ModelFile> files = new ArrayList<>();
 
   public FileSchemaTestClass _file(ModelFile _file) {
     this._file = _file;
diff --git a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/NullableClass.java b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/NullableClass.java
index 24871591e13..c5b47ae100b 100644
--- a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/NullableClass.java
+++ b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/NullableClass.java
@@ -81,7 +81,7 @@ public class NullableClass extends HashMap<String, Object>  {
 
   public static final String JSON_PROPERTY_ARRAY_ITEMS_NULLABLE = "array_items_nullable";
   @JsonProperty(JSON_PROPERTY_ARRAY_ITEMS_NULLABLE)
-  private List<Object> arrayItemsNullable;
+  private List<Object> arrayItemsNullable = new ArrayList<>();
 
   public static final String JSON_PROPERTY_OBJECT_NULLABLE_PROP = "object_nullable_prop";
   @JsonProperty(JSON_PROPERTY_OBJECT_NULLABLE_PROP)
diff --git a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ObjectWithDeprecatedFields.java b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ObjectWithDeprecatedFields.java
index fbefde29294..1f5b0440747 100644
--- a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ObjectWithDeprecatedFields.java
+++ b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/ObjectWithDeprecatedFields.java
@@ -51,7 +51,7 @@ public class ObjectWithDeprecatedFields   {
 
   public static final String JSON_PROPERTY_BARS = "bars";
   @JsonProperty(JSON_PROPERTY_BARS)
-  private List<String> bars;
+  private List<String> bars = new ArrayList<>();
 
   public ObjectWithDeprecatedFields uuid(String uuid) {
     this.uuid = uuid;
diff --git a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/Pet.java b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/Pet.java
index 6f0881cc9eb..0535435e3a8 100644
--- a/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/jaxrs/jersey3/src/gen/java/org/openapitools/model/Pet.java
@@ -61,7 +61,7 @@ public class Pet   {
 
   public static final String JSON_PROPERTY_TAGS = "tags";
   @JsonProperty(JSON_PROPERTY_TAGS)
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index 5d9620a9662..a07b9f5f5f8 100644
--- a/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -26,7 +26,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index deabc1c65e6..4513ec53877 100644
--- a/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -26,7 +26,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/ArrayTest.java
index 39be54311c7..3ea26158c18 100644
--- a/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/ArrayTest.java
@@ -26,13 +26,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/EnumArrays.java
index 46bf4157bde..d994343e973 100644
--- a/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/EnumArrays.java
@@ -98,7 +98,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index c5a92f52cff..e8a3362e07e 100644
--- a/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -28,7 +28,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/Pet.java
index bd36429fabc..5d5fd678a93 100644
--- a/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/Pet.java
@@ -40,7 +40,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/XmlItem.java
index 344d0d98546..eccca3318bf 100644
--- a/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/model/XmlItem.java
@@ -34,7 +34,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -45,10 +45,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -59,10 +59,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -73,10 +73,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -87,10 +87,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/spring-boot-nullable-set/src/main/java/org/openapitools/model/ObjectWithUniqueItems.java b/samples/server/petstore/spring-boot-nullable-set/src/main/java/org/openapitools/model/ObjectWithUniqueItems.java
index 953cb393508..2c0fd1d93e2 100644
--- a/samples/server/petstore/spring-boot-nullable-set/src/main/java/org/openapitools/model/ObjectWithUniqueItems.java
+++ b/samples/server/petstore/spring-boot-nullable-set/src/main/java/org/openapitools/model/ObjectWithUniqueItems.java
@@ -35,13 +35,13 @@ public class ObjectWithUniqueItems {
   private JsonNullable<Set<String>> nullSet = JsonNullable.<Set<String>>undefined();
 
   @Valid
-  private Set<String> notNullSet;
+  private Set<String> notNullSet = new LinkedHashSet<>();
 
   @Valid
   private JsonNullable<List<String>> nullList = JsonNullable.<List<String>>undefined();
 
   @Valid
-  private List<String> notNullList;
+  private List<String> notNullList = new ArrayList<>();
 
   @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME)
   private OffsetDateTime notNullDateField;
diff --git a/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index 6b232d75594..8c23c998d17 100644
--- a/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -26,7 +26,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index 97b899e1fc5..d1dd62698ee 100644
--- a/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -26,7 +26,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/ArrayTest.java
index 10114f3598c..24aba0d1d6e 100644
--- a/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/ArrayTest.java
@@ -26,13 +26,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/EnumArrays.java
index 4a5d6b82e8b..27567ba7bbd 100644
--- a/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/EnumArrays.java
@@ -98,7 +98,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index 16281a47737..7b7ec966a29 100644
--- a/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -28,7 +28,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/Pet.java
index 022924969ac..7678b3c576a 100644
--- a/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/Pet.java
@@ -40,7 +40,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/XmlItem.java
index 01d3a567547..0c3ef3b7daa 100644
--- a/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/springboot-beanvalidation-no-nullable/src/main/java/org/openapitools/model/XmlItem.java
@@ -34,7 +34,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -45,10 +45,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -59,10 +59,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -73,10 +73,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -87,10 +87,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index ca8f8a06383..831564f23bb 100644
--- a/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index 16ec232bf1b..7cffec68450 100644
--- a/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/ArrayTest.java
index 06a95f5bab8..430b0c0e25c 100644
--- a/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/ArrayTest.java
@@ -27,13 +27,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/EnumArrays.java
index 60084b81c39..f42059fd988 100644
--- a/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/EnumArrays.java
@@ -99,7 +99,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index ab3a340561e..ee88b88d408 100644
--- a/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -29,7 +29,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/Pet.java
index a28b5c88566..bcefb3bffc2 100644
--- a/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/Pet.java
@@ -41,7 +41,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/XmlItem.java
index ca34b6fce40..06b420cb3d4 100644
--- a/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/springboot-beanvalidation/src/main/java/org/openapitools/model/XmlItem.java
@@ -35,7 +35,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -46,10 +46,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -60,10 +60,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -74,10 +74,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -88,10 +88,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index ca8f8a06383..831564f23bb 100644
--- a/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index 16ec232bf1b..7cffec68450 100644
--- a/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/ArrayTest.java
index 06a95f5bab8..430b0c0e25c 100644
--- a/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/ArrayTest.java
@@ -27,13 +27,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/EnumArrays.java
index 60084b81c39..f42059fd988 100644
--- a/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/EnumArrays.java
@@ -99,7 +99,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index ab3a340561e..ee88b88d408 100644
--- a/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -29,7 +29,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/Pet.java
index a28b5c88566..bcefb3bffc2 100644
--- a/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/Pet.java
@@ -41,7 +41,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/XmlItem.java
index ca34b6fce40..06b420cb3d4 100644
--- a/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/springboot-delegate-j8/src/main/java/org/openapitools/model/XmlItem.java
@@ -35,7 +35,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -46,10 +46,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -60,10 +60,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -74,10 +74,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -88,10 +88,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/springboot-delegate-no-response-entity/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-delegate-no-response-entity/src/main/java/org/openapitools/model/Pet.java
index 516fff70474..dce6a41f893 100644
--- a/samples/server/petstore/springboot-delegate-no-response-entity/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-delegate-no-response-entity/src/main/java/org/openapitools/model/Pet.java
@@ -39,7 +39,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index ca8f8a06383..831564f23bb 100644
--- a/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index 16ec232bf1b..7cffec68450 100644
--- a/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayTest.java
index 06a95f5bab8..430b0c0e25c 100644
--- a/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/ArrayTest.java
@@ -27,13 +27,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/EnumArrays.java
index 60084b81c39..f42059fd988 100644
--- a/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/EnumArrays.java
@@ -99,7 +99,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index ab3a340561e..ee88b88d408 100644
--- a/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -29,7 +29,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/Pet.java
index a28b5c88566..bcefb3bffc2 100644
--- a/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/Pet.java
@@ -41,7 +41,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/XmlItem.java
index ca34b6fce40..06b420cb3d4 100644
--- a/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/springboot-delegate/src/main/java/org/openapitools/model/XmlItem.java
@@ -35,7 +35,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -46,10 +46,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -60,10 +60,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -74,10 +74,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -88,10 +88,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/springboot-implicitHeaders-annotationLibrary/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-implicitHeaders-annotationLibrary/src/main/java/org/openapitools/model/Pet.java
index 824c742e32f..c7857b3392a 100644
--- a/samples/server/petstore/springboot-implicitHeaders-annotationLibrary/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-implicitHeaders-annotationLibrary/src/main/java/org/openapitools/model/Pet.java
@@ -36,7 +36,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index ca8f8a06383..831564f23bb 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index 16ec232bf1b..7cffec68450 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayTest.java
index 06a95f5bab8..430b0c0e25c 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/ArrayTest.java
@@ -27,13 +27,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/EnumArrays.java
index 60084b81c39..f42059fd988 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/EnumArrays.java
@@ -99,7 +99,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index ab3a340561e..ee88b88d408 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -29,7 +29,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/Pet.java
index a28b5c88566..bcefb3bffc2 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/Pet.java
@@ -41,7 +41,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/XmlItem.java
index ca34b6fce40..06b420cb3d4 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/org/openapitools/model/XmlItem.java
@@ -35,7 +35,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -46,10 +46,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -60,10 +60,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -74,10 +74,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -88,10 +88,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/springboot-lombok-data/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-lombok-data/src/main/java/org/openapitools/model/Pet.java
index 6e2e916eaff..a0d4c905f7f 100644
--- a/samples/server/petstore/springboot-lombok-data/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-lombok-data/src/main/java/org/openapitools/model/Pet.java
@@ -42,7 +42,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-lombok-tostring/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-lombok-tostring/src/main/java/org/openapitools/model/Pet.java
index f94a6f28f61..e37ccc26187 100644
--- a/samples/server/petstore/springboot-lombok-tostring/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-lombok-tostring/src/main/java/org/openapitools/model/Pet.java
@@ -43,7 +43,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index ca8f8a06383..831564f23bb 100644
--- a/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index 16ec232bf1b..7cffec68450 100644
--- a/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/ArrayTest.java
index 06a95f5bab8..430b0c0e25c 100644
--- a/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/ArrayTest.java
@@ -27,13 +27,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/EnumArrays.java
index 60084b81c39..f42059fd988 100644
--- a/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/EnumArrays.java
@@ -99,7 +99,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index ab3a340561e..ee88b88d408 100644
--- a/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -29,7 +29,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/Pet.java
index a28b5c88566..bcefb3bffc2 100644
--- a/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/Pet.java
@@ -41,7 +41,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/XmlItem.java
index ca34b6fce40..06b420cb3d4 100644
--- a/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/model/XmlItem.java
@@ -35,7 +35,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -46,10 +46,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -60,10 +60,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -74,10 +74,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -88,10 +88,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index ca8f8a06383..831564f23bb 100644
--- a/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index 16ec232bf1b..7cffec68450 100644
--- a/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/ArrayTest.java
index 06a95f5bab8..430b0c0e25c 100644
--- a/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/ArrayTest.java
@@ -27,13 +27,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/EnumArrays.java
index 60084b81c39..f42059fd988 100644
--- a/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/EnumArrays.java
@@ -99,7 +99,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index ab3a340561e..ee88b88d408 100644
--- a/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -29,7 +29,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/Pet.java
index a28b5c88566..bcefb3bffc2 100644
--- a/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/Pet.java
@@ -41,7 +41,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/XmlItem.java
index ca34b6fce40..06b420cb3d4 100644
--- a/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/model/XmlItem.java
@@ -35,7 +35,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -46,10 +46,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -60,10 +60,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -74,10 +74,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -88,10 +88,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index ca8f8a06383..831564f23bb 100644
--- a/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index 16ec232bf1b..7cffec68450 100644
--- a/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/ArrayTest.java
index 06a95f5bab8..430b0c0e25c 100644
--- a/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/ArrayTest.java
@@ -27,13 +27,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/EnumArrays.java
index 60084b81c39..f42059fd988 100644
--- a/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/EnumArrays.java
@@ -99,7 +99,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index ab3a340561e..ee88b88d408 100644
--- a/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -29,7 +29,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/Pet.java
index d9fbcdac0dd..c3466886e61 100644
--- a/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/Pet.java
@@ -38,7 +38,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/XmlItem.java
index ca34b6fce40..06b420cb3d4 100644
--- a/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/springboot-spring-pageable-delegatePattern-without-j8/src/main/java/org/openapitools/model/XmlItem.java
@@ -35,7 +35,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -46,10 +46,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -60,10 +60,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -74,10 +74,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -88,10 +88,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index ca8f8a06383..831564f23bb 100644
--- a/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index 16ec232bf1b..7cffec68450 100644
--- a/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/ArrayTest.java
index 06a95f5bab8..430b0c0e25c 100644
--- a/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/ArrayTest.java
@@ -27,13 +27,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/EnumArrays.java
index 60084b81c39..f42059fd988 100644
--- a/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/EnumArrays.java
@@ -99,7 +99,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index ab3a340561e..ee88b88d408 100644
--- a/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -29,7 +29,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/Pet.java
index d9fbcdac0dd..c3466886e61 100644
--- a/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/Pet.java
@@ -38,7 +38,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/XmlItem.java
index ca34b6fce40..06b420cb3d4 100644
--- a/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/springboot-spring-pageable-delegatePattern/src/main/java/org/openapitools/model/XmlItem.java
@@ -35,7 +35,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -46,10 +46,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -60,10 +60,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -74,10 +74,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -88,10 +88,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index ca8f8a06383..831564f23bb 100644
--- a/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index 16ec232bf1b..7cffec68450 100644
--- a/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/ArrayTest.java
index 06a95f5bab8..430b0c0e25c 100644
--- a/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/ArrayTest.java
@@ -27,13 +27,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/EnumArrays.java
index 60084b81c39..f42059fd988 100644
--- a/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/EnumArrays.java
@@ -99,7 +99,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index ab3a340561e..ee88b88d408 100644
--- a/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -29,7 +29,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/Pet.java
index d9fbcdac0dd..c3466886e61 100644
--- a/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/Pet.java
@@ -38,7 +38,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/XmlItem.java
index ca34b6fce40..06b420cb3d4 100644
--- a/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/springboot-spring-pageable-without-j8/src/main/java/org/openapitools/model/XmlItem.java
@@ -35,7 +35,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -46,10 +46,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -60,10 +60,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -74,10 +74,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -88,10 +88,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index ca8f8a06383..831564f23bb 100644
--- a/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index 16ec232bf1b..7cffec68450 100644
--- a/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/ArrayTest.java
index 06a95f5bab8..430b0c0e25c 100644
--- a/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/ArrayTest.java
@@ -27,13 +27,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/EnumArrays.java
index 60084b81c39..f42059fd988 100644
--- a/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/EnumArrays.java
@@ -99,7 +99,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index ab3a340561e..ee88b88d408 100644
--- a/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -29,7 +29,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/Pet.java
index d9fbcdac0dd..c3466886e61 100644
--- a/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/Pet.java
@@ -38,7 +38,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/XmlItem.java
index ca34b6fce40..06b420cb3d4 100644
--- a/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/springboot-spring-pageable/src/main/java/org/openapitools/model/XmlItem.java
@@ -35,7 +35,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -46,10 +46,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -60,10 +60,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -74,10 +74,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -88,10 +88,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/springboot-spring-provide-args/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-spring-provide-args/src/main/java/org/openapitools/model/Pet.java
index add3e5f2412..37bfa240a0b 100644
--- a/samples/server/petstore/springboot-spring-provide-args/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-spring-provide-args/src/main/java/org/openapitools/model/Pet.java
@@ -37,7 +37,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
index ca8f8a06383..831564f23bb 100644
--- a/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
index 16ec232bf1b..7cffec68450 100644
--- a/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/ArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/ArrayTest.java b/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/ArrayTest.java
index 06a95f5bab8..430b0c0e25c 100644
--- a/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/ArrayTest.java
@@ -27,13 +27,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/EnumArrays.java b/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/EnumArrays.java
index d167793289d..9cbe5994d18 100644
--- a/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/EnumArrays.java
@@ -99,7 +99,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = Optional.of(justSymbol);
diff --git a/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/FileSchemaTestClass.java b/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/FileSchemaTestClass.java
index 1eaa720f77b..09b786508ac 100644
--- a/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/FileSchemaTestClass.java
@@ -29,7 +29,7 @@ public class FileSchemaTestClass {
   private Optional<File> file = Optional.empty();
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = Optional.of(file);
diff --git a/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/Pet.java b/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/Pet.java
index 5c2f776f732..4399ca1963d 100644
--- a/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/Pet.java
+++ b/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/Pet.java
@@ -41,7 +41,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/XmlItem.java b/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/XmlItem.java
index e3ee0d32111..5cc8d406847 100644
--- a/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/XmlItem.java
+++ b/samples/server/petstore/springboot-useoptional/src/main/java/org/openapitools/model/XmlItem.java
@@ -35,7 +35,7 @@ public class XmlItem {
   private Optional<Boolean> attributeBoolean = Optional.empty();
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private Optional<String> nameString = Optional.empty();
 
@@ -46,10 +46,10 @@ public class XmlItem {
   private Optional<Boolean> nameBoolean = Optional.empty();
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private Optional<String> prefixString = Optional.empty();
 
@@ -60,10 +60,10 @@ public class XmlItem {
   private Optional<Boolean> prefixBoolean = Optional.empty();
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private Optional<String> namespaceString = Optional.empty();
 
@@ -74,10 +74,10 @@ public class XmlItem {
   private Optional<Boolean> namespaceBoolean = Optional.empty();
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private Optional<String> prefixNsString = Optional.empty();
 
@@ -88,10 +88,10 @@ public class XmlItem {
   private Optional<Boolean> prefixNsBoolean = Optional.empty();
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = Optional.of(attributeString);
diff --git a/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/ArrayOfArrayOfNumberOnly.java
index 1322caff81d..f38fb852bec 100644
--- a/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/ArrayOfArrayOfNumberOnly.java
@@ -26,7 +26,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnly {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/ArrayOfNumberOnly.java
index 59d0d26e96e..ab06ee421f8 100644
--- a/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/ArrayOfNumberOnly.java
@@ -26,7 +26,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnly {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/ArrayTest.java b/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/ArrayTest.java
index 89aaf45030d..374ec939a91 100644
--- a/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/ArrayTest.java
@@ -26,13 +26,13 @@ import javax.annotation.Generated;
 public class ArrayTest {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/EnumArrays.java b/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/EnumArrays.java
index 9c95bc47b9a..4ce9f1f2bd2 100644
--- a/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/EnumArrays.java
@@ -98,7 +98,7 @@ public class EnumArrays {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/FileSchemaTestClass.java b/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/FileSchemaTestClass.java
index 930e236a360..385e668aaba 100644
--- a/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/FileSchemaTestClass.java
+++ b/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/FileSchemaTestClass.java
@@ -28,7 +28,7 @@ public class FileSchemaTestClass {
   private File file;
 
   @Valid
-  private List<@Valid File> files;
+  private List<@Valid File> files = new ArrayList<>();
 
   public FileSchemaTestClass file(File file) {
     this.file = file;
diff --git a/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/Pet.java b/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/Pet.java
index 23c68eddbfb..581cb6b1991 100644
--- a/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/Pet.java
+++ b/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/Pet.java
@@ -40,7 +40,7 @@ public class Pet {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   @Valid
-  private List<@Valid Tag> tags;
+  private List<@Valid Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/XmlItem.java b/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/XmlItem.java
index 81a60410c7e..dbac01163b5 100644
--- a/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/XmlItem.java
+++ b/samples/server/petstore/springboot-virtualan/src/main/java/org/openapitools/virtualan/model/XmlItem.java
@@ -34,7 +34,7 @@ public class XmlItem {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -45,10 +45,10 @@ public class XmlItem {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -59,10 +59,10 @@ public class XmlItem {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -73,10 +73,10 @@ public class XmlItem {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -87,10 +87,10 @@ public class XmlItem {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItem attributeString(String attributeString) {
     this.attributeString = attributeString;
diff --git a/samples/server/petstore/springboot/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnlyDto.java b/samples/server/petstore/springboot/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnlyDto.java
index 30e377f04a9..211448697f1 100644
--- a/samples/server/petstore/springboot/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnlyDto.java
+++ b/samples/server/petstore/springboot/src/main/java/org/openapitools/model/ArrayOfArrayOfNumberOnlyDto.java
@@ -29,7 +29,7 @@ import javax.annotation.Generated;
 public class ArrayOfArrayOfNumberOnlyDto {
 
   @Valid
-  private List<List<BigDecimal>> arrayArrayNumber;
+  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<>();
 
   public ArrayOfArrayOfNumberOnlyDto arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
diff --git a/samples/server/petstore/springboot/src/main/java/org/openapitools/model/ArrayOfNumberOnlyDto.java b/samples/server/petstore/springboot/src/main/java/org/openapitools/model/ArrayOfNumberOnlyDto.java
index 166fc7dc600..20c2b629599 100644
--- a/samples/server/petstore/springboot/src/main/java/org/openapitools/model/ArrayOfNumberOnlyDto.java
+++ b/samples/server/petstore/springboot/src/main/java/org/openapitools/model/ArrayOfNumberOnlyDto.java
@@ -29,7 +29,7 @@ import javax.annotation.Generated;
 public class ArrayOfNumberOnlyDto {
 
   @Valid
-  private List<BigDecimal> arrayNumber;
+  private List<BigDecimal> arrayNumber = new ArrayList<>();
 
   public ArrayOfNumberOnlyDto arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
diff --git a/samples/server/petstore/springboot/src/main/java/org/openapitools/model/ArrayTestDto.java b/samples/server/petstore/springboot/src/main/java/org/openapitools/model/ArrayTestDto.java
index 5df0933b017..2f920052636 100644
--- a/samples/server/petstore/springboot/src/main/java/org/openapitools/model/ArrayTestDto.java
+++ b/samples/server/petstore/springboot/src/main/java/org/openapitools/model/ArrayTestDto.java
@@ -29,13 +29,13 @@ import javax.annotation.Generated;
 public class ArrayTestDto {
 
   @Valid
-  private List<String> arrayOfString;
+  private List<String> arrayOfString = new ArrayList<>();
 
   @Valid
-  private List<List<Long>> arrayArrayOfInteger;
+  private List<List<Long>> arrayArrayOfInteger = new ArrayList<>();
 
   @Valid
-  private List<List<@Valid ReadOnlyFirstDto>> arrayArrayOfModel;
+  private List<List<@Valid ReadOnlyFirstDto>> arrayArrayOfModel = new ArrayList<>();
 
   public ArrayTestDto arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
diff --git a/samples/server/petstore/springboot/src/main/java/org/openapitools/model/EnumArraysDto.java b/samples/server/petstore/springboot/src/main/java/org/openapitools/model/EnumArraysDto.java
index a69bfa5c475..de8e04215ea 100644
--- a/samples/server/petstore/springboot/src/main/java/org/openapitools/model/EnumArraysDto.java
+++ b/samples/server/petstore/springboot/src/main/java/org/openapitools/model/EnumArraysDto.java
@@ -101,7 +101,7 @@ public class EnumArraysDto {
   }
 
   @Valid
-  private List<ArrayEnumEnum> arrayEnum;
+  private List<ArrayEnumEnum> arrayEnum = new ArrayList<>();
 
   public EnumArraysDto justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
diff --git a/samples/server/petstore/springboot/src/main/java/org/openapitools/model/FileSchemaTestClassDto.java b/samples/server/petstore/springboot/src/main/java/org/openapitools/model/FileSchemaTestClassDto.java
index 05c0cfaf55f..e6e2c5534de 100644
--- a/samples/server/petstore/springboot/src/main/java/org/openapitools/model/FileSchemaTestClassDto.java
+++ b/samples/server/petstore/springboot/src/main/java/org/openapitools/model/FileSchemaTestClassDto.java
@@ -31,7 +31,7 @@ public class FileSchemaTestClassDto {
   private FileDto file;
 
   @Valid
-  private List<@Valid FileDto> files;
+  private List<@Valid FileDto> files = new ArrayList<>();
 
   public FileSchemaTestClassDto file(FileDto file) {
     this.file = file;
diff --git a/samples/server/petstore/springboot/src/main/java/org/openapitools/model/PetDto.java b/samples/server/petstore/springboot/src/main/java/org/openapitools/model/PetDto.java
index cb2d0933fe7..11a8e81b310 100644
--- a/samples/server/petstore/springboot/src/main/java/org/openapitools/model/PetDto.java
+++ b/samples/server/petstore/springboot/src/main/java/org/openapitools/model/PetDto.java
@@ -43,7 +43,7 @@ public class PetDto {
   private Set<String> photoUrls = new LinkedHashSet<>();
 
   @Valid
-  private List<@Valid TagDto> tags;
+  private List<@Valid TagDto> tags = new ArrayList<>();
 
   /**
    * pet status in the store
diff --git a/samples/server/petstore/springboot/src/main/java/org/openapitools/model/XmlItemDto.java b/samples/server/petstore/springboot/src/main/java/org/openapitools/model/XmlItemDto.java
index 144a7e34167..9815bd0baf0 100644
--- a/samples/server/petstore/springboot/src/main/java/org/openapitools/model/XmlItemDto.java
+++ b/samples/server/petstore/springboot/src/main/java/org/openapitools/model/XmlItemDto.java
@@ -37,7 +37,7 @@ public class XmlItemDto {
   private Boolean attributeBoolean;
 
   @Valid
-  private List<Integer> wrappedArray;
+  private List<Integer> wrappedArray = new ArrayList<>();
 
   private String nameString;
 
@@ -48,10 +48,10 @@ public class XmlItemDto {
   private Boolean nameBoolean;
 
   @Valid
-  private List<Integer> nameArray;
+  private List<Integer> nameArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> nameWrappedArray;
+  private List<Integer> nameWrappedArray = new ArrayList<>();
 
   private String prefixString;
 
@@ -62,10 +62,10 @@ public class XmlItemDto {
   private Boolean prefixBoolean;
 
   @Valid
-  private List<Integer> prefixArray;
+  private List<Integer> prefixArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixWrappedArray;
+  private List<Integer> prefixWrappedArray = new ArrayList<>();
 
   private String namespaceString;
 
@@ -76,10 +76,10 @@ public class XmlItemDto {
   private Boolean namespaceBoolean;
 
   @Valid
-  private List<Integer> namespaceArray;
+  private List<Integer> namespaceArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> namespaceWrappedArray;
+  private List<Integer> namespaceWrappedArray = new ArrayList<>();
 
   private String prefixNsString;
 
@@ -90,10 +90,10 @@ public class XmlItemDto {
   private Boolean prefixNsBoolean;
 
   @Valid
-  private List<Integer> prefixNsArray;
+  private List<Integer> prefixNsArray = new ArrayList<>();
 
   @Valid
-  private List<Integer> prefixNsWrappedArray;
+  private List<Integer> prefixNsWrappedArray = new ArrayList<>();
 
   public XmlItemDto attributeString(String attributeString) {
     this.attributeString = attributeString;