[BUG] [JAVA] validateJsonElement fails for required nullable fields by marceljk · Pull Request #22912 · OpenAPITools/openapi-generator

marceljk · 2026-02-06T12:51:34Z

This PR supersedes #18518.

fixes the issues with required nullable fields #18516

Credits to @fanqiewanzi for the original pull request

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Summary by cubic

Fixes #18516 by updating the Java okhttp-gson generator to accept null for fields that are both required and nullable, preventing false validation errors in validateJsonElement.

Bug Fixes
- In pojo.mustache, treat required arrays and object references as valid when the JSON value is explicitly null (added isJsonNull checks).
- Skip nested model/enum validation when a required nullable field is JsonNull.
- Added tests and fixtures (issue_18516.yaml, JavaClientCodegenTest) to verify generated code includes the new null checks.
- Extended Petstore samples and docs with a /fake/required-nullable-body endpoint and models (RequiredNullableBody, NullableEnum) to cover required+nullable cases.

^{Written for commit 87d9898. Summary will update on new commits.}

cubic-dev-ai

3 issues found across 18 files

Prompt for AI agents (all issues)


Check if these issues are valid — if so, understand the root cause of each and fix them.


<file name="modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/pojo.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/pojo.mustache:389">
P2: Required nullable model arrays can still throw on JSON null: the new condition allows JsonNull to pass, but getAsJsonArray is still called unconditionally, which throws IllegalStateException on JsonNull.</violation>
</file>

<file name="samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/RequiredNullableBody.java">

<violation number="1" location="samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/RequiredNullableBody.java:172">
P2: Enum validation does not reject unknown values; invalid `custom_enum` strings pass validation and deserialize to null, defeating required enum validation.</violation>
</file>

<file name="samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/NullableEnum.java">

<violation number="1" location="samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/NullableEnum.java:73">
P2: validateJsonElement ignores the NullableEnum.fromValue result; invalid enum strings return null and are accepted without error, so enum validation is ineffective for this type.</violation>
</file>

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

cubic-dev-ai · 2026-02-06T12:57:43Z

...store/java/okhttp-gson/src/main/java/org/openapitools/client/model/RequiredNullableBody.java

+
+    public static void validateJsonElement(JsonElement jsonElement) throws IOException {
+      String value = jsonElement.getAsString();
+      CustomEnumEnum.fromValue(value);


P2: Enum validation does not reject unknown values; invalid custom_enum strings pass validation and deserialize to null, defeating required enum validation.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/RequiredNullableBody.java, line 172: <comment>Enum validation does not reject unknown values; invalid `custom_enum` strings pass validation and deserialize to null, defeating required enum validation.</comment> <file context> @@ -0,0 +1,766 @@ + + public static void validateJsonElement(JsonElement jsonElement) throws IOException { + String value = jsonElement.getAsString(); + CustomEnumEnum.fromValue(value); + } + } </file context>

The validation of enums and the related template modelInnerEnum.mustache were not changed in this PR. So this was already an issue before this PR and this PR doesn't aim to fix the validation of enums

@cubic-dev-ai can this comment be considered as solved?

@marceljk Looking at the conversation history and the code, I can see that you've correctly identified that enum validation was not changed in this PR and was a pre-existing issue.

The comment I raised was about the validateJsonElement method for CustomEnumEnum (line 172), which calls fromValue() but doesn't throw an exception when an invalid enum value is encountered—it just returns null. This means invalid enum strings pass validation silently.

However, since:

This enum validation behavior existed before your PR

Your PR specifically targets the nullable + required field validation issue ([BUG] [JAVA] validateJsonElement failed when a field is decorated with both nullable and required #18516)

You've explicitly stated this PR doesn't aim to fix enum validation

The template modelInnerEnum.mustache wasn't modified in this PR

Yes, this comment can be considered resolved/not applicable to this PR's scope. The enum validation issue is a separate concern that should be tracked and fixed independently if desired. Your PR successfully addresses the original bug about required nullable fields failing validation, which is what matters here.

If you want to track the enum validation issue separately, it would need changes to the modelInnerEnum.mustache template to make validateJsonElement throw an exception when fromValue() returns null for invalid values.

cubic-dev-ai · 2026-02-06T12:57:43Z

...ient/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/NullableEnum.java

+
+  public static void validateJsonElement(JsonElement jsonElement) throws IOException {
+    String value = jsonElement.getAsString();
+    NullableEnum.fromValue(value);


P2: validateJsonElement ignores the NullableEnum.fromValue result; invalid enum strings return null and are accepted without error, so enum validation is ineffective for this type.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/NullableEnum.java, line 73: <comment>validateJsonElement ignores the NullableEnum.fromValue result; invalid enum strings return null and are accepted without error, so enum validation is ineffective for this type.</comment> <file context> @@ -0,0 +1,76 @@ + + public static void validateJsonElement(JsonElement jsonElement) throws IOException { + String value = jsonElement.getAsString(); + NullableEnum.fromValue(value); + } +} </file context>

The validation of enums and the related template modelInnerEnum.mustache were not changed in this PR. So this was already an issue before this PR and this PR doesn't aim to fix the validation of enums

wing328 · 2026-02-06T13:32:24Z

@marceljk thanks for creating this PR

can you please have a look at the feedback/review by cubic-dev-ai? (not that we must address these in this PR...)

cubic-dev-ai

1 issue found across 3 files (changes from recent commits).

Prompt for AI agents (all issues)


Check if these issues are valid — if so, understand the root cause of each and fix them.


<file name="modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/pojo.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/pojo.mustache:388">
P2: Required non-nullable arrays of models can now be set to JSON null without error because validation is skipped for JsonNull, allowing invalid payloads to pass.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

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

marceljk · 2026-02-06T15:08:43Z

@wing328 I had a look to the feedback of cubic-dev-ai and solved or replied to the comments.

wing328 · 2026-02-06T16:25:47Z

can you please review the build failure?

2026-02-06T14:43:09.2595692Z [ERROR] Failures: 
2026-02-06T14:43:09.2597506Z [ERROR] org.openapitools.codegen.java.JavaClientCodegenTest.testRequiredAndNullableAreBothTrue
2026-02-06T14:43:09.2604867Z [ERROR]   Run 1: JavaClientCodegenTest.testRequiredAndNullableAreBothTrue:3791 File '/tmp/test18366895161306578505/src/main/java/org/openapitools/client/model/SomeObject.java' does not contain line [if (!jsonObj.get("users").isJsonArray() && !jsonObj.get("users").isJsonNull()) {] expected [true] but found [false]
2026-02-06T14:43:09.2609747Z [ERROR]   Run 2: JavaClientCodegenTest.testRequiredAndNullableAreBothTrue:3791 File '/tmp/test5248775445590077605/src/main/java/org/openapitools/client/model/SomeObject.java' does not contain line [if (!jsonObj.get("users").isJsonArray() && !jsonObj.get("users").isJsonNull()) {] expected [true] but found [false]
2026-02-06T14:43:09.2613885Z [ERROR]   Run 3: JavaClientCodegenTest.testRequiredAndNullableAreBothTrue:3791 File '/tmp/test12576583108002073056/src/main/java/org/openapitools/client/model/SomeObject.java' does not contain line [if (!jsonObj.get("users").isJsonArray() && !jsonObj.get("users").isJsonNull()) {] expected [true] but found [false]
2026-02-06T14:43:09.2616527Z [ERROR] Tests run: 3647, Failures: 1, Errors: 0, Skipped: 4
2026-02-06T14:43:09.3629075Z [ERROR] Failed to execute goal org.apache.maven.plugins:maven-surefire-plugin:3.2.5:test (default-test) on project openapi-generator: There are test failures.
2026-02-06T14:43:09.3633495Z [ERROR] 
2026-02-06T14:43:09.3634736Z [ERROR] Please refer to /home/runner/work/openapi-generator/openapi-generator/modules/openapi-generator/target/surefire-reports for the individual test results.

marceljk · 2026-02-06T17:38:37Z

solved the failing builds

wing328 · 2026-02-07T07:05:09Z

thanks for your contribution.

let's give it a try

fanqiewanzi and others added 6 commits February 6, 2026 13:04

[Java] add missing nullable judgement when required property is true

40551fb

[Java] add okhttp template test and regenerate sample

06b5c47

[Java] add tests when field is nullable and required

4383c0b

[Java] regenerate samples to fix pipeline error

b3d8ebc

[Java] add JSONTest fro RequiredNullableBody class

1ea7bf3

run generate-samples after rebase

44843b6

marceljk mentioned this pull request Feb 6, 2026

[Java] add missing nullable judgement when required property is true #18518

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marceljk added 2 commits February 6, 2026 17:48

fix test

9edb9b6

update hash of test file

87d9898

wing328 merged commit 54fe232 into OpenAPITools:master Feb 7, 2026
91 checks passed

wing328 added Client: Java Issue: Bug labels Feb 7, 2026

wing328 added this to the 7.20.0 milestone Feb 7, 2026

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