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.
