Omit null OpenAPI response descriptions

[Copilot]

Pull Request

Description

OpenAPI response descriptions must be strings when present. Responses with no description were serialized as "description": null, which Swagger Editor rejects.

"200": {}

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe):

Related Issue(s)

Changes Made

• Serialization
  • Omit description from OpenApiResponse when Description is null.
• Coverage
  • Added response serialization coverage for OpenAPI 2.0, 3.0, 3.1, and 3.2.
• Expectations
  • Updated affected operation serialization baselines.

Testing

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed
• All existing tests pass

Checklist

• My code follows the code style of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Versions applicability

• My change applies to the version 1.X of the library, if so PR link:
• My change applies to the version 2.X of the library, if so PR link:
• My change applies to the version 3.X of the library, if so PR link:
• I have evaluated the applicability of my change against the other versions above.

Additional Notes

None.

• Fixes Description in Response cannot be null #3069