def assemble(self, header_json, metadata_json, content_json):
        ''' Create a Message instance assembled from json fragments.

        Args:
            header_json (JSON) :
            metadata_json (JSON) :
            content_json (JSON) :

        Returns:
            message

        '''
        header = json_decode(header_json)
        if header not in 'msgtype':
            log.error("Bad header with no msgtype was: %r", header)
            raise ProtocolError("No 'msgtype' in header")
        return self._messages[header['msgtype']].assemble(
            header_json, metadata_json, content_json
        )
dataset/ETHPy150Open bokeh/bokeh/bokeh/server/protocol/__init__.py/Protocol.assemble/swapped operands of `not in`