def _BUFFER_PAYLOAD(self, fragment: Fragment) -> None:
        payload = self._assume_binary(fragment)
        if self._buf_header is None:
            raise ValidationError("Consuming a buffer payload, but current buffer header is None")
        header = BufferHeader(id=self._buf_header["id"])
        cast(Message[Any], self._partial).assemble_buffer(header, payload)

        self._check_complete()