code: public void removeChannelFromCache(long channelId) {
          channels.computeIfPresent(channelId, (key, channel) -> {
              if (channel instanceof Cleanupable) {
                  ((Cleanupable) channel).cleanup();
              }
              return null;
          });
      }
docs: Removes a channel from the cache.
  
  @param channelId The id of the channel to remove.