fix(typescript-fetch): filter Null type from oneOf to prevent missing model references

[guizmaii]

Problem

In OpenAPI 3.1, oneOf can include type: 'null' to represent nullable unions:

NullableResult:
  oneOf:
    - $ref: '#/components/schemas/FileLocation'
    - $ref: '#/components/schemas/DetailedLocation'
    - type: 'null'

The codegen maps type: 'null' to a model named "Null" and adds it to the oneOf variants list. However, no Null.ts model file is ever generated, causing TypeScript import errors:

error TS2305: Module '"../models/index"' has no exported member 'Null'.
error TS2724: '"../models/index"' has no exported member named 'NullFromJSON'.
error TS2724: '"../models/index"' has no exported member named 'NullToJSON'.

Solution

Filter "Null" from cm.oneOf and cm.oneOfModels during model post-processing in TypeScriptFetchClientCodegen.processCodeGenModel(), and set cm.isNullable = true instead.

This follows the same pattern already used by the C#, Java, and PowerShell generators:

• CSharpClientCodegen.java:1670
• JavaClientCodegen.java:1207-1210
• PowerShellClientCodegen.java:1098-1101

Test plan

• Added testNullableOneOfDoesNotImportNullModel test with a new spec (nullable-oneOf.yaml) that uses type: 'null' in a oneOf
• Verifies no Null imports/references in the generated model file
• Verifies no Null.ts model file is generated
• Verifies the union type only contains valid model types
• All 23 TypeScriptFetchClientCodegenTest tests pass

---

Summary by cubic

Fixes typescript-fetch codegen to handle OpenAPI 3.1 type: 'null' correctly. oneOf unions now use | null, and operations that returned Null are generated as void, removing broken imports.

• Bug Fixes
  • Filter "Null" from cm.oneOf/oneOfModels; set cm.isNullable = true and update modelOneOfInterfaces.mustache to append | null.
  • Convert operations with returnType === 'Null' to void and remove Null from operation and file-level imports.
  • Add tests: nullable-oneOf.yaml to verify unions include only real models plus | null with no Null.ts, and null-response.yaml to ensure null responses become void.

^{Written for commit cda4b15. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files

[cubic-dev-ai]

1 issue found across 1 file (changes from recent commits).

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/TypeScriptFetchClientCodegen.java">

<violation number="1" location="modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/TypeScriptFetchClientCodegen.java:721">
P2: Unconditional `"Null"` return-type rewrite can erase legitimate user-defined `Null` response models and remove needed imports.</violation>
</file>

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