Prevent PydanticUserError

[oxesoft]

In the generated ApiClient.send method, TypeAdapter(type_) will raise a PydanticUserError if type_ is None. This occurs for API endpoints that return no content (e.g., 204 No Content). Additionally, the method should return None when type_ is None to remain consistent with the method's overloads.

                if type_ is None:
                    return None
                adapter = TypeAdapter(type_)
                if type_ == bytes:
                    return adapter.validate_python(response.content)
                return adapter.validate_python(response.json())

Originally posted by @gemini-code-assist[bot] in #86 (comment)