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

* Fix optional empty collection as default

* Fix test

* Fix test

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;

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;

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;

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;

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;

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

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;