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## 5.0.4

**`(fix):`** Fix optional complex-type parameters in multipart file upload requests being
sent as `"null"` instead of being omitted. When an optional body property
(e.g., `Optional[List[str]]`, `Optional[Any]`) defaults to `OMIT`,
`json.dumps(jsonable_encoder(OMIT))` was evaluating to the string `"null"`,
destroying the OMIT sentinel before `remove_omit_from_dict` could strip it.
Optional non-primitive body properties now emit a ternary guard
(`json.dumps(...) if prop is not OMIT else OMIT`) so that the OMIT sentinel
is preserved and correctly removed from the request data.