docs: @Handler(channels = Self.class)
      public void onRegistered(NioRegistration.Completed event)
              throws InterruptedException, IOException {
          NioHandler handler = event.event().handler();
          if (handler == this) {
              if (event.event().get() == null) {
                  fire(new Error(event,
                      "Registration failed, no NioDispatcher?"));
                  return;
              }
              registration = event.event().get();
              purger = new Purger();
              purger.start();
              fire(new Ready(serverSocketChannel.getLocalAddress()));
              return;
          }
          if (handler instanceof TcpChannelImpl) {
              TcpChannelImpl channel = (TcpChannelImpl) handler;
              channel.downPipeline()
                  .fire(new Accepted(channel.nioChannel().getLocalAddress(),
                      channel.nioChannel().getRemoteAddress(), false,
                      Collections.emptyList()), channel);
              channel.registrationComplete(event.event());
          }
      }