code: public final TcpServer doOnUnbound(Consumer<? super DisposableServer> doOnUnbind) {
  		Objects.requireNonNull(doOnUnbind, "doOnUnbound");
  		return new TcpServerDoOn(this, null, null, doOnUnbind);
  	}
docs: Setups a callback called when {@link io.netty.channel.ServerChannel} is
  unbound.
  
  @param doOnUnbind a consumer observing server stop event
  
  @return a new {@link TcpServer}