[java] Appropriate instantiation of model with dynamic properties

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

@@ -809,6 +809,13 @@ public String toDefaultValue(Schema schema) {
 
             return String.format(Locale.ROOT, pattern, typeDeclaration);
         } else if (ModelUtils.isMapSchema(schema) && !(schema instanceof ComposedSchema)) {
+            if (schema.getProperties() != null && schema.getProperties().size() > 0) {
+                // object is complex object with free-form additional properties
+                if (schema.getDefault() != null) {
+                    return super.toDefaultValue(schema);
+                }
+                return null;
+            }
             final String pattern;
             if (fullJavaUtil) {
                 pattern = "new java.util.HashMap<%s>()";

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

@@ -26,6 +26,7 @@
 import java.time.format.DateTimeFormatter;
 import java.util.Date;
 import org.openapitools.codegen.CodegenConstants;
+import org.openapitools.codegen.CodegenModel;
 import org.openapitools.codegen.CodegenType;
 import org.openapitools.codegen.TestUtils;
 import org.openapitools.codegen.languages.AbstractJavaCodegen;
@@ -524,6 +525,55 @@ public void processOptsBooleanFalseFromNumeric() {
         Assert.assertFalse((boolean) codegen.additionalProperties().get(CodegenConstants.SNAPSHOT_VERSION));
     }
 
+    @Test
+    public void nullDefaultValueForModelWithDynamicProperties() {
+        final P_AbstractJavaCodegen codegen = new P_AbstractJavaCodegen();
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/mapSchemas.yaml");
+        codegen.additionalProperties().put(CodegenConstants.GENERATE_ALIAS_AS_MODEL, true);
+        codegen.setOpenAPI(openAPI);
+
+        Schema schema = openAPI.getComponents().getSchemas().get("ModelWithAdditionalProperties");
+        CodegenModel cm = codegen.fromModel("ModelWithAdditionalProperties", schema);
+        Assert.assertEquals(cm.vars.size(), 1, "Expected single declared var");
+        Assert.assertEquals(cm.vars.get(0).name, "id");
+        Assert.assertNull(cm.defaultValue, "Expected no defined default value in spec");
+
+        String defaultValue = codegen.toDefaultValue(schema);
+        Assert.assertNull(defaultValue);
+    }
+
+    @Test
+    public void maplikeDefaultValueForModelWithStringToStringMapping() {
+        final P_AbstractJavaCodegen codegen = new P_AbstractJavaCodegen();
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/mapSchemas.yaml");
+        codegen.additionalProperties().put(CodegenConstants.GENERATE_ALIAS_AS_MODEL, true);
+        codegen.setOpenAPI(openAPI);
+
+        Schema schema = openAPI.getComponents().getSchemas().get("ModelWithStringToStringMapping");
+        CodegenModel cm = codegen.fromModel("ModelWithAdditionalProperties", schema);
+        Assert.assertEquals(cm.vars.size(), 0, "Expected no declared vars");
+        Assert.assertNull(cm.defaultValue, "Expected no defined default value in spec");
+
+        String defaultValue = codegen.toDefaultValue(schema);
+        Assert.assertEquals(defaultValue, "new HashMap<String, String>()", "Expected string-string map aliased model to default to new HashMap<String, String>()");
+    }
+
+    @Test
+    public void maplikeDefaultValueForModelWithStringToModelMapping() {
+        final P_AbstractJavaCodegen codegen = new P_AbstractJavaCodegen();
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/mapSchemas.yaml");
+        codegen.additionalProperties().put(CodegenConstants.GENERATE_ALIAS_AS_MODEL, true);
+        codegen.setOpenAPI(openAPI);
+
+        Schema schema = openAPI.getComponents().getSchemas().get("ModelWithStringToModelMapping");
+        CodegenModel cm = codegen.fromModel("ModelWithStringToModelMapping", schema);
+        Assert.assertEquals(cm.vars.size(), 0, "Expected no declared vars");
+        Assert.assertNull(cm.defaultValue, "Expected no defined default value in spec");
+
+        String defaultValue = codegen.toDefaultValue(schema);
+        Assert.assertEquals(defaultValue, "new HashMap<String, ComplexModel>()", "Expected string-ref map aliased model to default to new HashMap<String, ComplexModel>()");
+    }
+
     private static Schema<?> createObjectSchemaWithMinItems() {
         return new ObjectSchema()
                 .addProperties("id", new IntegerSchema().format("int32"))

modules/openapi-generator/src/test/resources/3_0/mapSchemas.yaml

@@ -0,0 +1,71 @@
+openapi: "3.0.0"
+info:
+  title: Example API
+  version: "3.0.0"
+paths:
+  /:
+    get:
+      summary: Empty Route
+      responses:
+        "200":
+          description: Good Request.
+          content:
+            application/json:
+              schema:
+                type: array
+                items:
+                  $ref: '#/components/schemas/FreeformObjectTypes'
+        "400":
+          description: Bad Request.
+        "403":
+          description: Forbidden. Access denied.
+
+components:
+  schemas:
+    ExampleModel:
+      type: object
+      properties:
+        id:
+          type: string
+        withAdditinalProperties:
+          $ref: '#/components/schemas/ModelWithAdditionalProperties'
+    ModelWithAdditionalProperties:
+      type: object
+      properties:
+        id:
+          type: string
+      additionalProperties: {}
+    ModelWithStringToStringMapping:
+      type: object
+      additionalProperties:
+        type: string
+    ModelWithStringToModelMapping:
+      type: object
+      additionalProperties:
+        $ref: '#/components/schemas/ComplexModel'
+    ComplexModel:
+      type: object
+      properties:
+        id:
+          type: integer
+          format: int64
+        name:
+          type: string
+      required:
+        - name
+      example:
+        name: Puma
+        id: 1
+    FreeformObjectTypes:
+      type: object
+      properties:
+        ExampleModel:
+          $ref: '#/components/schemas/ExampleModel'
+        ModelWithAdditionalProperties:
+          $ref: '#/components/schemas/ModelWithAdditionalProperties'
+        ModelWithStringToStringMapping:
+          $ref: '#/components/schemas/ModelWithStringToStringMapping'
+        ModelWithStringToModelMapping:
+          $ref: '#/components/schemas/ModelWithStringToModelMapping'
+        ComplexModel:
+          $ref: '#/components/schemas/ComplexModel'