[Inf1mum]

Fixes #24393

Context

#24393 reports that the okhttp-gson CustomTypeAdapterFactory in pojo.mustache throws
java.lang.IllegalStateException: Not a JSON Object: null when a model with additionalProperties: true
serializes an undeclared property whose value is null (e.g. an unknown field deserialized from a
server response that was JSON null): gson.toJsonTree(null) returns JsonNull.INSTANCE and the
else branch called getAsJsonObject() on it.

The template guard proposed in the issue is already on master: it was merged in #24573 (based on
#24395), which added the jsonElement.isJsonNull() check writing JsonNull.INSTANCE plus the
com.google.gson.JsonNull import, and regenerated the samples. That PR did not reference #24393
and did not add tests, which left the issue open without regression coverage.

This PR closes that gap with tests only, so the issue can be closed on merge. No template or
generated-sample changes are needed.

Changes (tests only)

• modules/openapi-generator/src/test/resources/3_0/java/okhttp-gson-null-additional-properties.yaml:
  minimal spec with an additionalProperties: true model.
• modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaOkHttpGsonNullAdditionalPropertiesTest.java:
  generates that model with the java/okhttp-gson generator, compiles the generated
  CustomTypeAdapterFactory against the real Gson runtime (same fixture approach as
  JavaOkHttpGsonOneOfPrimitiveArrayTest), and asserts:
  • serializing a null undeclared-property value writes JSON null instead of throwing
    Not a JSON Object: null, both at JsonElement level and in full text output;
  • deserializing JSON null undeclared properties stores a null-valued entry in additionalProperties;
  • serialize -> deserialize -> serialize round trip preserves the null entry;
  • the existing String/array/object branches keep their behavior (follow-up to [BUG][java] CustomTypeAdapterFactory incorrectly assumes non-primitives are json objects #14404/[java] fix for json arrays #17812).
• samples/client/petstore/java/okhttp-gson/src/test/java/org/openapitools/client/JSONTest.java:
  new testAdditionalPropertiesNullValue reproducing the issue's exact repro with the generated
  petstore AdditionalPropertiesClass (putAdditionalProperty("unknownField", null) + toJson()).

Regenerated samples

None required. This PR contains no template changes; the okhttp-gson samples already carry the
JsonNull guard since #24573, and re-running ./bin/generate-samples.sh bin/configs/java-okhttp-gson.yaml
on this branch produces no diff in samples/client/petstore/java/okhttp-gson (verified).

Verification

• ./mvnw -pl modules/openapi-generator -am test -Dtest=JavaOkHttpGsonNullAdditionalPropertiesTest passes.
• mvn test -Dtest=JSONTest in samples/client/petstore/java/okhttp-gson passes (34 tests, including the new one).

PR checklist

• Read the contribution guidelines.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  Tests-only PR: the project modules and CLI jar were built with ./mvnw package -DskipTests,
  and the targeted regen ./bin/generate-samples.sh bin/configs/java-okhttp-gson.yaml produces
  no diff on this branch (see "Regenerated samples" above). All changed files are committed.
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.
  (@mentions intentionally omitted)

---

Summary by cubic

Adds regression tests for the already-merged fix to #24393, where the okhttp-gson CustomTypeAdapterFactory threw IllegalStateException: Not a JSON Object: null when serializing a null undeclared-property value. The fix shipped in #24573 without test coverage; this tests-only PR closes that gap so the issue can be closed. No template changes or sample regeneration needed.

• Generator-level test generates an additionalProperties: true model plus the client's JSON factory, compiles both against the real Gson runtime, and verifies a serialize → deserialize → serialize round trip with a null value through the generated JSON.getGson(), plus unchanged behavior for string/array/object values. Adds gson-fire and okio (pinned to 3.2.0 so its Kotlin metadata stays readable by the module's test compiler) as test-scoped dependencies; jsr305 stays transitive from guava so the main compile classpath is unaffected.
• Sample test reproduces the issue's exact repro using the petstore AdditionalPropertiesClass.
• Updates the sample test fingerprint record for JSONTest.java to match the modified file.

^{Written for commit 7bf3c79. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 3 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. When an issue isn't valid or won't be fixed in this PR, reply in its thread with the reason and then resolve the thread. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="samples/client/petstore/java/okhttp-gson/src/test/java/org/openapitools/client/JSONTest.java">

<violation number="1" location="samples/client/petstore/java/okhttp-gson/src/test/java/org/openapitools/client/JSONTest.java:788">
P3: `deserialized` is populated from unrelated hard-coded JSON, so this does not exercise the claimed serialize→deserialize→serialize path. Parse the serialized output instead, and initialize `map_property` on `model` if that field must remain asserted.</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

View guided diff | Re-trigger cubic</sub>

[cubic-dev-ai]

P3: deserialized is populated from unrelated hard-coded JSON, so this does not exercise the claimed serialize→deserialize→serialize path. Parse the serialized output instead, and initialize map_property on model if that field must remain asserted.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. When an issue isn't valid or won't be fixed in this PR, reply in its thread with the reason and then resolve the thread. At samples/client/petstore/java/okhttp-gson/src/test/java/org/openapitools/client/JSONTest.java, line 788:

<comment>`deserialized` is populated from unrelated hard-coded JSON, so this does not exercise the claimed serialize→deserialize→serialize path. Parse the serialized output instead, and initialize `map_property` on `model` if that field must remain asserted.</comment>

<file context>
@@ -765,6 +765,39 @@ public void testAdditionalArrayProperties() throws IOException {
+        assertFalse(model.toJson().contains("unknownField"));
+
+        // deserialize: JSON null undeclared properties are stored as null-valued entries
+        AdditionalPropertiesClass deserialized = AdditionalPropertiesClass.fromJson("{\"map_property\":{\"key\":\"value\"},\"unknownField\":null}");
+        assertEquals(deserialized.getMapProperty(), Collections.singletonMap("key", "value"));
+        assertTrue(deserialized.getAdditionalProperties().containsKey("unknownField"));
</file context>

[Inf1mum]

Fixed in 349bca4: the generator-side test (JavaOkHttpGsonNullAdditionalPropertiesTest) now runs the full serialize -> deserialize -> serialize round-trip through the client's configured Gson. It generates the client (model + supporting JSON factory), compiles the generated sources against the real Gson runtime (gson-fire, okio and jsr305 added as test-scoped dependencies of the generator module) and takes the Gson from the generated JSON.getGson() instead of a hand-built builder over a model stub. A model instance with a null-valued additionalProperties entry is serialized, the resulting JSON is fed back into fromJson, the null entry is asserted to survive the round trip, and re-serialization is asserted byte-stable; the existing no-throw-on-serialize assertion is kept. The generator-side test and the sample JSONTest (34 tests) both pass locally.

[Inf1mum]

The Build: JDK 11/17 / Build / Windows tests failures on 349bca4 were caused by this PR's own pom change, not by master: declaring com.google.code.findbugs:jsr305 directly at test scope made Maven mediate the transitive compile-scope jsr305 (brought by guava) down to test scope, so javax.annotation.Nullable left the main compile classpath — exactly the three codegen classes that import it (AbstractPythonCodegen, AbstractRustCodegen, K6ClientCodegen) failed with "package javax.annotation does not exist".

Fixed in 1ebfe98 by removing the direct jsr305 declaration (the generated okhttp-gson sources still resolve javax.annotation.Nullable from the transitive compile-scope artifact, which also covers the test classpath). Verified locally that modules/openapi-generator main compile plus the new JavaOkHttpGsonNullAdditionalPropertiesTest pass. Sample outputs are unchanged, so no test_file_list.yaml fingerprint update is needed.