'Convert a message into JSON for sending to a sibling cell.'

def to_json(self):

    _dict = self._to_dict()
    _dict['ctxt'] = _dict['ctxt'].to_dict()
    method_kwargs = _dict['method_kwargs']
    for (k, v) in method_kwargs.items():
        method_kwargs[k] = self.serializer.serialize_entity(self.ctxt, v)
    return jsonutils.dumps(_dict)
