fix(typescript-fetch): optional nullable fields return null instead of undefined

[mstojanovic8]

When an optional field is marked as nullable in the spec, FromJSONTyped now returns null (not undefined) when the API returns null. Non-nullable optional fields continue to return undefined as before.

Fixes #5670

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cc @TiFu @taxpon @sebastianhaas @kenisteward @Vrolijkx @macjohnny @topce @akehir @petejohansonxo @amakhrov @davidgamero @mkusaka @joscha @dennisameling

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Summary by cubic

Make typescript-fetch models return null for optional nullable fields when the API sends null, and undefined when the field is missing. Non-nullable optionals are unchanged. Fixes #5670.

• Bug Fixes

  • Use strict checks (=== undefined / === null) in modelGeneric.mustache so FromJSONTyped distinguishes missing vs explicit null across primitives, dates, arrays/sets, maps, free-form objects, and object refs.
  • Added test testOptionalNullableFieldDeserializesToNull with nullable_property.json; regenerated petstore typescript-fetch samples.
  • Updated samples/server/petstore/jaxrs-spec-enum/pom.xml to JUnit 5 (org.junit.jupiter) and maven-surefire-plugin/maven-failsafe-plugin 3.5.6 for reliable test runs.

• Migration

  • If you relied on undefined for optional nullable fields, update checks to handle null (e.g., nullish coalescing). Missing fields still return undefined; non-nullable optional and required fields are unchanged.

^{Written for commit 1196727. Summary will update on new commits.}

[cubic-dev-ai]

4 issues found across 17 files

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

Re-trigger cubic</sub>

[macjohnny]

thanks for the fix

[mstojanovic8]

thanks for the fix

Thanks for the quick review! Looking forward to seeing this in the next release 🙌

[wing328]

@mstojanovic8 thanks for the PR

can you please review the build failure when you've time?

let us know if you need help updating the samples