Fix default empty collections when collection is optional

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java

@@ -1178,8 +1178,8 @@ public String toDefaultValue(CodegenProperty cp, Schema schema) {
         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)) {

modules/openapi-generator/src/test/java/org/openapitools/codegen/java/AbstractJavaCodegenTest.java

@@ -605,11 +605,11 @@ public void toDefaultValueTest() {
 
         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"));

modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaModelEnumTest.java

@@ -75,7 +75,7 @@ public void converterInArrayTest() {
         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 void converterInArrayInArrayTest() {
         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);
 

modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaModelTest.java

@@ -130,7 +130,7 @@ public void listPropertyTest() {
         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 void setPropertyTest() {
         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 void list2DPropertyTest() {
         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 void complexListPropertyTest() {
         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 void complexArrayPropertyTest() {
         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 void complexSetPropertyTest() {
         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 void arrayModelWithItemNameTest() {
         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 void modelWithWrappedXmlTest() {
         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);

modules/openapi-generator/src/test/java/org/openapitools/codegen/java/spring/SpringCodegenTest.java

@@ -4518,4 +4518,34 @@ public void testLombokAnnotations() throws IOException {
                 .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<>();");
+
+    }
 }

samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/DefaultValue.java

@@ -99,7 +99,7 @@ public static ArrayStringEnumDefaultEnum fromValue(String value) {
   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();

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

samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java

@@ -39,7 +39,7 @@
 @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() {
   }