When authoring a session-ful channel, it’s important to signal “end of session” correctly so that the runtime (or any other user of the channel) knows when to stop reading messages, and to start shutting down his side of the conversation (with CloseOutputSession and/or channel.Close). A null Message/RequestContext signals end-of-session to the caller. In particular, depending on your channel shape, you should do the following:

• IInputSessionChannel/IDuplexSessionChannel: Return null from channel.Receive(). Correspondingly, return true from TryReceive with the “message” out-param set to null. And of course, cover your bases by having BeginTryReceive complete synchronously with a signal to return true + message = null from EndTryReceive.
• IRequestSessionChannel: Return null from channel.ReceiveRequest(). Correspondingly, return true from TryReceiveRequest with the “context” out-param set to null. Lastly, have BeginTryReceiveRequest complete synchronously with a signal to return true + context = null from EndTryReceiveRequest.