If the sender is not `null`, then we can send.
No need for a flag, and assert() in the sending method.
If the sender is `null`, then the sending code will not able to invoke it.
Types FTW :-)
Change-Id: I7d153ba014c578a73dce2eab28aceedbb8814711
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/298440
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Konstantin Shcheglov
8d2bafa624