docs: def _handle_ping(self, packet, protocol):
          """ Responds to pings from registry_client only if the node_ids present in the ping payload are registered
  
          :param packet: The 'ping' packet received
          :param protocol: The protocol on which the pong should be sent
          """
          if 'payload' in packet:
              is_valid_node = True
              node_ids = list(packet['payload'].values())
              for node_id in node_ids:
                  if self._repository.get_node(node_id) is None:
                      is_valid_node = False
                      break
              if is_valid_node:
                  self._pong(packet, protocol)
          else:
              self._pong(packet, protocol)