@alexvaluyskiy can you rebase on dev please? And please squash your commits per the contributors guidelines. Thx for effort!

@Danthar done

The failing unit test is a race condition. i verified that it works locally.

Ok, we have a a consistently failing MNTK spec.

Akka.Remote.Tests.MultiNode.RemoteNodeRestartDeathWatchMultiNode1.Must_receive_terminated_when_remote_actor_system_is_restarted

This needs to be investigated and fixed before this PR can be merged.

Needs to be rebased :(

Since alot of fixes has been made to the MNTK. Could you please rebase on the latest dev? Some of the issues reported in this thread might 'magically' fix themselves now ;)

Restarted test builds. Tests still failing.

Throws a NullReferenceException inside the PatternSpec.GracefulStop specs

@Aaronontheweb It throws NullReferenceException, because the new DeadLetter should not be created, if Sender is null. But gracefulStop send NoSender

@alexvaluyskiy @Aaronontheweb Oh I found what caused this problem.

Akka seems to keep sender not-null in packing a message into the Envelop. AbstractDispatcher.scala

object Envelope { 
  def apply(message: Any, sender: ActorRef, system: ActorSystem): Envelope = { 
    if (message == null) throw new InvalidMessageException("Message is null") 
      new Envelope(message, if (sender ne Actor.noSender) sender else system.deadLetters) 
  } 
} 

But Akka.NET doesn't do like this. It just packs a message into Envelop without changes and
it keeps Envelope.Sender null if sender is null.

var m = new Envelope {
  Sender = sender,
  Message = message,
};

This looks like a fundamental difference and should be considered.

@Aaronontheweb what do you think about last commit?

@Horusiath this test "FSharp.Tests.ApiTests.actor that accepts unit will receive unit message" sends an empty message. But never versions of Akka Jvm forbid it, as @veblush mentioned before. How could we change this test?

If nullish values are going to be explicitly forbidden, then that test is no longer needed. However this also means, that it's a breaking change and should be mentioned as that in release notes.

Looks good!. Links back to: #2160