Attach a callback on the job pubsub if it exists

def listen_to_node(self, id_):
        """Attach a callback on the job pubsub if it exists"""
        if r_client.get(id_) is None:
            return
        else:
            self.toredis.subscribe(_pubsub_key(id_), callback=self.callback)
            self._listening_to[_pubsub_key(id_)] = id_
            return id_