code: public B channel(Class<? extends C> channelClass) {
          if (channelClass == null) {
              throw new NullPointerException("channelClass");
          }
          return channelFactory(new ReflectiveChannelFactory<C>(channelClass));
      }
docs: The {@link Class} which is used to create {@link Channel} instances from.
  You either use this or {@link #channelFactory(io.netty.channel.ChannelFactory)} if your
  {@link Channel} implementation has no no-args constructor.