You never retained the message, are you sure you should be releasing it? That seems really strange to me. Look at this:

https://github.com/netty/netty/blob/4.0/transport/src/main/java/io/netty/channel/SimpleChannelInboundHandler.java#L110

They already release it. I don't know of any reference counting mechanism where you are obligated to release something you never retained.