code: func Open(URL ...string) (pubsub.Hub, error) {
  	if len(URL) == 0 {
  		URL = []string{nats.DefaultURL}
  	}
  
  	log.Info("connecting to nats hub: %v", URL)
  
  	conn, err := nats.Connect(URL[0])
  	if err != nil {
  		return nil, err
  	}
  
  	return &hub{
  		conn: conn,
  		subs: make(map[*sub]struct{}),
  	}, nil
  }
docs: // Open creates pubsub hub connected to nats server.