Fixes for NoSender serialization bugs

[ssoshchepkov]

Fixes for NoSender actor serialization bugs described in #1036.

[Aaronontheweb]

thanks, @ssoshchepkov - looks like we've overlooked this one.

[rogeralsing]

Im not sure this fix is correct.
The scala version of the code uses the old "/nosender" path.
I think there could be more to this than we see here

[Aaronontheweb]

@rogeralsing ok, I reverted it. I'll let you take a closer look and see what's really going on.

[rogeralsing]

Turns out that its NoBody that uses that notation in scala.
NoSender in scala is just a wrapper for null

@ssoshchepkov if you want, could you adapt the PR to treat NoSender as null instead?
It's better if we stay as close as possible to the Scala code.

  /**
   * Default placeholder (null) used for "!" to indicate that there is no sender of the message,
   * that will be translated to the receiving system's deadLetters.
   */
  final val noSender: ActorRef = null

[Aaronontheweb]

@rogeralsing won't that conflict with your PR that turns null into NoSender? :p

[rogeralsing]

That code could just go away if we do this.
There is no reason to have weird comparisons all over the codebase if nosender really means null imo.

Or?

[ssoshchepkov]

@rogeralsing I've made changes to treat NoSender as null. Could you reopen this PR? Or should I create another?

[rogeralsing]

I think you have to send a fresh one. I dont think a PR can be re-opened once merged (as this was merged and then a revert patch applied)