docs: protected <X extends MessageDispatcher> X installUpHandler(UpHandler handler, boolean canReplace) {
          UpHandler existing = channel.getUpHandler();
          if (existing == null)
              channel.setUpHandler(handler);
          else if(canReplace) {
              log.warn("Channel already has an up handler installed (%s) but now it is being overridden", existing);
              channel.setUpHandler(handler);
          }
          return (X)this;
      }