Fix default empty collections when collection is optional (#18080)

* Fix optional empty collection as default

* Fix test

* Fix test

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;

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;

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;

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;

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;

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

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;