Don't remove null type if a default is present.

[luhn]

Changes

Fixes #2144

Fixes #2055

How to Review

Pretty straightforward PR

Checklist

• Unit tests updated
• docs/ updated (if necessary)
• pnpm run update:examples run (only applicable for openapi-typescript)

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[ben-xD]

This is nice, can we merge it @htunnicliff?

[danielkv]

+1

[duncanbeevers]

The maintainers team is looking at this issue and its corresponding PR.
Please refrain from adding +1 comments.