def content_type(self) -> str | None:
        """The content type for the request.  Reflected from and to
        the :attr:`headers`.  Do not set if you set :attr:`files` or
        :attr:`form` for auto detection.
        """
        ct = self.headers.get("Content-Type")
        if ct is None and not self._input_stream:
            if self._files:
                return "multipart/form-data"
            if self._form:
                return "application/x-www-form-urlencoded"
            return None
        return ct
The content type for the request.  Reflected from and to
        the :attr:`headers`.  Do not set if you set :attr:`files` or
        :attr:`form` for auto detection.
        
src/werkzeug/test.py