[BUG] [JAVA] validateJsonElement fails for required nullable fields

modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/pojo.mustache

@@ -386,7 +386,7 @@ public class {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{{#vendorExtens
       {{#items.isModel}}
       {{#required}}
       // ensure the json data is an array
-      if (!jsonObj.get("{{{baseName}}}").isJsonArray()) {
+      if (!jsonObj.get("{{{baseName}}}").isJsonArray(){{#isNullable}} && !jsonObj.get("{{baseName}}").isJsonNull(){{/isNullable}}) {
         throw new IllegalArgumentException(String.format(java.util.Locale.ROOT, "Expected the field `{{{baseName}}}` to be an array in the JSON string but got `%s`", jsonObj.get("{{{baseName}}}").toString()));
       }
 
@@ -424,7 +424,7 @@ public class {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{{#vendorExtens
       // ensure the required json array is present
       if (jsonObj.get("{{{baseName}}}") == null) {
         throw new IllegalArgumentException("Expected the field `linkedContent` to be an array in the JSON string but got `null`");
-      } else if (!jsonObj.get("{{{baseName}}}").isJsonArray()) {
+      } else if (!jsonObj.get("{{{baseName}}}").isJsonArray(){{#isNullable}} && !jsonObj.get("{{baseName}}").isJsonNull(){{/isNullable}}) {
         throw new IllegalArgumentException(String.format(java.util.Locale.ROOT, "Expected the field `{{{baseName}}}` to be an array in the JSON string but got `%s`", jsonObj.get("{{{baseName}}}").toString()));
       }
       {{/required}}
@@ -438,8 +438,14 @@ public class {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{{#vendorExtens
       {{/isString}}
       {{#isModel}}
       {{#required}}
+      {{#isNullable}}
+      if (jsonObj.get("{{{baseName}}}") != null && !jsonObj.get("{{{baseName}}}").isJsonNull()) {
+      {{/isNullable}}
       // validate the required field `{{{baseName}}}`
       {{{dataType}}}.validateJsonElement(jsonObj.get("{{{baseName}}}"));
+      {{#isNullable}}
+      }
+      {{/isNullable}}
       {{/required}}
       {{^required}}
       // validate the optional field `{{{baseName}}}`
@@ -450,8 +456,14 @@ public class {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{{#vendorExtens
       {{/isModel}}
       {{#isEnum}}
       {{#required}}
+      {{#isNullable}}
+      if (jsonObj.get("{{{baseName}}}") != null && !jsonObj.get("{{{baseName}}}").isJsonNull()) {
+      {{/isNullable}}
       // validate the required field `{{{baseName}}}`
       {{{datatypeWithEnum}}}.validateJsonElement(jsonObj.get("{{{baseName}}}"));
+      {{#isNullable}}
+      }
+      {{/isNullable}}
       {{/required}}
       {{^required}}
       // validate the optional field `{{{baseName}}}`
@@ -462,8 +474,14 @@ public class {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{{#vendorExtens
       {{/isEnum}}
       {{#isEnumRef}}
       {{#required}}
+      {{#isNullable}}
+      if (jsonObj.get("{{{baseName}}}") != null && !jsonObj.get("{{{baseName}}}").isJsonNull()) {
+      {{/isNullable}}
       // validate the required field `{{{baseName}}}`
       {{{dataType}}}.validateJsonElement(jsonObj.get("{{{baseName}}}"));
+      {{#isNullable}}
+      }
+      {{/isNullable}}
       {{/required}}
       {{^required}}
       // validate the optional field `{{{baseName}}}`

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

@@ -3769,6 +3769,34 @@ public void testClassesAreValidJavaOkHttpGson() {
         );
     }
 
+    @Test
+    public void testRequiredAndNullableAreBothTrue() throws IOException {
+        File output = Files.createTempDirectory("test").toFile();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("java")
+                .setLibrary(JavaClientCodegen.OKHTTP_GSON)
+                .setInputSpec("src/test/resources/bugs/issue_18516.yaml")
+                .setOutputDir(output.getAbsolutePath().replace("\\", "/"));
+
+
+        DefaultGenerator generator = new DefaultGenerator();
+        List<File> files = generator.opts(configurator.toClientOptInput()).generate();
+        files.forEach(File::deleteOnExit);
+
+        validateJavaSourceFiles(files);
+
+        Path modelFile = Paths.get(output + "/src/main/java/org/openapitools/client/model/SomeObject.java");
+        TestUtils.assertFileContains(
+                modelFile,
+                "} else if (!jsonObj.get(\"ids\").isJsonArray()  && !jsonObj.get(\"ids\").isJsonNull()) {",
+                "if (!jsonObj.get(\"users\").isJsonArray() && !jsonObj.get(\"users\").isJsonNull()) {",
+                "if (jsonObj.get(\"user\") != null && !jsonObj.get(\"user\").isJsonNull()) {",
+                "if (jsonObj.get(\"role\") != null && !jsonObj.get(\"role\").isJsonNull()) {",
+                "if (jsonObj.get(\"custom\") != null && !jsonObj.get(\"custom\").isJsonNull()) {");
+    }
+
     @Test(description = "Issue #21051")
     public void givenComplexObjectHasDefaultValueWhenGenerateThenDefaultAssignmentsAreValid() throws Exception {
         File output = Files.createTempDirectory("test").toFile().getCanonicalFile();

modules/openapi-generator/src/test/resources/3_0/java/petstore-with-fake-endpoints-models-for-testing-okhttp-gson.yaml

@@ -1369,6 +1369,19 @@ paths:
                 $ref: '#/components/schemas/Variable'
         '400':
           description: Invalid Value
+  /fake/required-nullable-body:
+    get:
+      tags:
+        - fake
+      summary: fields in the response body, required and nullable are both true
+      description: ''
+      responses:
+        '200':
+          description: success
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/RequiredNullableBody'
 servers:
   - url: 'http://{server}.swagger.io:{port}/v2'
     description: petstore server
@@ -2768,6 +2781,38 @@ components:
           $ref: '#/components/schemas/ArrayOneOf'
         anyof_prop:
           $ref: '#/components/schemas/ArrayAnyOf'
+    NullableEnum:
+      type: string
+      nullable: true
+      enum:
+        - custom
+    RequiredNullableBody:
+      allOf:
+        - $ref: '#/components/schemas/NullableClass'
+        - type: object
+          required:
+            - custom_ref_enum
+            - custom_enum
+            - integer_prop
+            - number_prop
+            - boolean_prop
+            - string_prop
+            - date_prop
+            - datetime_prop
+            - array_nullable_prop
+            - array_and_items_nullable_prop
+            - array_items_nullable
+            - object_nullable_prop
+            - object_and_items_nullable_prop
+            - object_items_nullable
+          properties:
+            custom_ref_enum:
+              $ref: "#/components/schemas/NullableEnum"
+            custom_enum:
+              type: string
+              nullable: true
+              enum:
+                - custom
     NestedArrayWithDefaultValues:
       type: object
       properties:

modules/openapi-generator/src/test/resources/bugs/issue_18516.yaml

@@ -0,0 +1,61 @@
+openapi: 3.0.3
+info:
+  title: test
+  description: Test API
+  version: 1.0.1
+
+paths:
+  /test:
+    get:
+      responses:
+        200:
+          description: Valid response
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/SomeObject"
+
+components:
+  schemas:
+    SomeObject:
+      type: object
+      required: 
+        - ids
+        - users
+        - user
+        - role
+        - custom
+      properties:
+        ids:
+          type: array
+          nullable: true
+          items:
+            type: integer
+        users:
+          type: array
+          nullable: true
+          items:
+            type: object
+            properties:
+              id:
+                type: string
+        user:
+          type: object
+          nullable: true
+          properties:
+            id:
+              type: string
+        role:
+          type: string
+          nullable: true
+          enum:
+            - admin
+            - tenant
+        custom:
+          $ref: "#/components/schemas/customEnum"
+    customEnum:
+      type: string
+      nullable: true
+      enum:
+        - custom
+

samples/client/petstore/java/okhttp-gson-nullable-required/src/main/java/org/openapitools/client/model/PetWithRequiredNullableCases1.java

@@ -424,7 +424,7 @@ public static void validateJsonElement(JsonElement jsonElement) throws IOExcepti
       // ensure the required json array is present
       if (jsonObj.get("photoUrls") == null) {
         throw new IllegalArgumentException("Expected the field `linkedContent` to be an array in the JSON string but got `null`");
-      } else if (!jsonObj.get("photoUrls").isJsonArray()) {
+      } else if (!jsonObj.get("photoUrls").isJsonArray() && !jsonObj.get("photoUrls").isJsonNull()) {
         throw new IllegalArgumentException(String.format(java.util.Locale.ROOT, "Expected the field `photoUrls` to be an array in the JSON string but got `%s`", jsonObj.get("photoUrls").toString()));
       }
       if (jsonObj.get("tags") != null && !jsonObj.get("tags").isJsonNull()) {

samples/client/petstore/java/okhttp-gson/.openapi-generator/FILES

@@ -79,6 +79,7 @@ docs/NewPet.md
 docs/NewPetCategoryInlineAllof.md
 docs/NewPetCategoryInlineAllofAllOfCategoryTag.md
 docs/NullableClass.md
+docs/NullableEnum.md
 docs/NullableShape.md
 docs/NumberOnly.md
 docs/ObjectWithDeprecatedFields.md
@@ -100,6 +101,7 @@ docs/PropertyNameCollision.md
 docs/Quadrilateral.md
 docs/QuadrilateralInterface.md
 docs/ReadOnlyFirst.md
+docs/RequiredNullableBody.md
 docs/Scalar.md
 docs/ScalarAnyOf.md
 docs/ScaleneTriangle.md
@@ -228,6 +230,7 @@ src/main/java/org/openapitools/client/model/NewPet.java
 src/main/java/org/openapitools/client/model/NewPetCategoryInlineAllof.java
 src/main/java/org/openapitools/client/model/NewPetCategoryInlineAllofAllOfCategoryTag.java
 src/main/java/org/openapitools/client/model/NullableClass.java
+src/main/java/org/openapitools/client/model/NullableEnum.java
 src/main/java/org/openapitools/client/model/NullableShape.java
 src/main/java/org/openapitools/client/model/NumberOnly.java
 src/main/java/org/openapitools/client/model/ObjectWithDeprecatedFields.java
@@ -248,6 +251,7 @@ src/main/java/org/openapitools/client/model/PropertyNameCollision.java
 src/main/java/org/openapitools/client/model/Quadrilateral.java
 src/main/java/org/openapitools/client/model/QuadrilateralInterface.java
 src/main/java/org/openapitools/client/model/ReadOnlyFirst.java
+src/main/java/org/openapitools/client/model/RequiredNullableBody.java
 src/main/java/org/openapitools/client/model/Scalar.java
 src/main/java/org/openapitools/client/model/ScalarAnyOf.java
 src/main/java/org/openapitools/client/model/ScaleneTriangle.java

samples/client/petstore/java/okhttp-gson/README.md

@@ -127,6 +127,7 @@ Class | Method | HTTP request | Description
 *FakeApi* | [**fakeOuterNumberSerialize**](docs/FakeApi.md#fakeOuterNumberSerialize) | **POST** /fake/outer/number | 
 *FakeApi* | [**fakeOuterStringSerialize**](docs/FakeApi.md#fakeOuterStringSerialize) | **POST** /fake/outer/string | 
 *FakeApi* | [**fakeRefParameter**](docs/FakeApi.md#fakeRefParameter) | **POST** /fake/pet/{petId}/reference/parameter | fake reference parameter
+*FakeApi* | [**fakeRequiredNullableBodyGet**](docs/FakeApi.md#fakeRequiredNullableBodyGet) | **GET** /fake/required-nullable-body | fields in the response body, required and nullable are both true
 *FakeApi* | [**fakeUploadRefRequestBodies**](docs/FakeApi.md#fakeUploadRefRequestBodies) | **POST** /fake/pet/{petId}/uploadImage | fake reference parameter
 *FakeApi* | [**getFakeArrayofenums**](docs/FakeApi.md#getFakeArrayofenums) | **GET** /fake/array-of-enums | Array of Enums
 *FakeApi* | [**getFakeHealth**](docs/FakeApi.md#getFakeHealth) | **GET** /fake/health | Health check endpoint
@@ -240,6 +241,7 @@ Class | Method | HTTP request | Description
  - [NewPetCategoryInlineAllof](docs/NewPetCategoryInlineAllof.md)
  - [NewPetCategoryInlineAllofAllOfCategoryTag](docs/NewPetCategoryInlineAllofAllOfCategoryTag.md)
  - [NullableClass](docs/NullableClass.md)
+ - [NullableEnum](docs/NullableEnum.md)
  - [NullableShape](docs/NullableShape.md)
  - [NumberOnly](docs/NumberOnly.md)
  - [ObjectWithDeprecatedFields](docs/ObjectWithDeprecatedFields.md)
@@ -260,6 +262,7 @@ Class | Method | HTTP request | Description
  - [Quadrilateral](docs/Quadrilateral.md)
  - [QuadrilateralInterface](docs/QuadrilateralInterface.md)
  - [ReadOnlyFirst](docs/ReadOnlyFirst.md)
+ - [RequiredNullableBody](docs/RequiredNullableBody.md)
  - [Scalar](docs/Scalar.md)
  - [ScalarAnyOf](docs/ScalarAnyOf.md)
  - [ScaleneTriangle](docs/ScaleneTriangle.md)

samples/client/petstore/java/okhttp-gson/api/openapi.yaml

@@ -1494,6 +1494,21 @@ paths:
       x-internal: true
       x-accepts:
       - application/json
+  /fake/required-nullable-body:
+    get:
+      description: ""
+      responses:
+        "200":
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/RequiredNullableBody"
+          description: success
+      summary: "fields in the response body, required and nullable are both true"
+      tags:
+      - fake
+      x-accepts:
+      - application/json
 components:
   parameters:
     pet_id:
@@ -2870,6 +2885,62 @@ components:
         anyof_prop:
           $ref: "#/components/schemas/ArrayAnyOf"
       type: object
+    NullableEnum:
+      enum:
+      - custom
+      nullable: true
+      type: string
+    RequiredNullableBody:
+      allOf:
+      - $ref: "#/components/schemas/NullableClass"
+      - properties:
+          custom_ref_enum:
+            $ref: "#/components/schemas/NullableEnum"
+          custom_enum:
+            enum:
+            - custom
+            nullable: true
+            type: string
+        required:
+        - array_and_items_nullable_prop
+        - array_items_nullable
+        - array_nullable_prop
+        - boolean_prop
+        - custom_enum
+        - custom_ref_enum
+        - date_prop
+        - datetime_prop
+        - integer_prop
+        - number_prop
+        - object_and_items_nullable_prop
+        - object_items_nullable
+        - object_nullable_prop
+        - string_prop
+        type: object
+      example:
+        number_prop: 6.027456183070403
+        datetime_prop: 2000-01-23T04:56:07.000+00:00
+        custom_ref_enum: custom
+        boolean_prop: true
+        string_prop: string_prop
+        array_nullable_prop:
+        - "{}"
+        - "{}"
+        custom_enum: custom
+        integer_prop: 0
+        array_and_items_nullable_prop:
+        - "{}"
+        - "{}"
+        object_items_nullable:
+          key: "{}"
+        object_nullable_prop:
+          key: "{}"
+        object_and_items_nullable_prop:
+          key: "{}"
+        date_prop: 2000-01-23
+        array_items_nullable:
+        - "{}"
+        - "{}"
     NestedArrayWithDefaultValues:
       properties:
         nestedArray: