code: public final <T> TcpServer selectorAttr(AttributeKey<T> key, T value) {
  		Objects.requireNonNull(key, "key");
  		return bootstrap(b -> b.attr(key, value));
  	}
docs: Injects default attribute to the future {@link io.netty.channel.ServerChannel}
  selector connection.
  
  @param key the attribute key
  @param value the attribute value
  @param <T> the attribute type
  
  @return a new {@link TcpServer}
  
  @see ServerBootstrap#attr(AttributeKey, Object)