code: public NettyChannelBuilder eventLoopGroup(@Nullable EventLoopGroup eventLoopGroup) {
      if (eventLoopGroup != null) {
        return eventLoopGroupPool(new FixedObjectPool<>(eventLoopGroup));
      }
      return eventLoopGroupPool(DEFAULT_EVENT_LOOP_GROUP_POOL);
    }
docs: Provides an EventGroupLoop to be used by the netty transport.
  
  <p>It's an optional parameter. If the user has not provided an EventGroupLoop when the channel
  is built, the builder will use the default one which is static.
  
  <p>You must also provide corresponding {@link #channelType(Class)} or {@link
  #channelFactory(ChannelFactory)} corresponding to the given {@code EventLoopGroup}. For
  example, {@link io.netty.channel.nio.NioEventLoopGroup} requires {@link NioSocketChannel}
  
  <p>The channel won't take ownership of the given EventLoopGroup. It's caller's responsibility
  to shut it down when it's desired.