code: public void addChannel(WebSocketChannel channel) {
          Objects.requireNonNull(channel, Required.CHANNEL.toString());
  
          final String url = RequestUtils.getWebSocketURL(channel);
          Set<WebSocketChannel> channels = getChannels(url);
          if (channels == null) {
              channels = new HashSet<>();
              channels.add(channel);
          } else {
              channels.add(channel);
          }
          setChannels(url, channels);
      }
docs: Adds a new channel to the manager
  
  @param channel channel The channel to put