docs: @Handler(channels = Self.class)
      public void onRegistered(NioRegistration.Completed event)
              throws InterruptedException, IOException {
          NioHandler handler = event.event().handler();
          if (!(handler instanceof TcpChannelImpl)) {
              return;
          }
          if (event.event().get() == null) {
              fire(new Error(event, "Registration failed, no NioDispatcher?",
                  new Throwable()));
              return;
          }
          TcpChannelImpl channel = (TcpChannelImpl) handler;
          channel.registrationComplete(event.event());
          channel.downPipeline()
              .fire(new Connected(channel.nioChannel().getLocalAddress(),
                  channel.nioChannel().getRemoteAddress()), channel);
      }