Update 2021/03/03: With the release of Dart 2.12, Dart supports sound null safety. Had to wait about ten years, but I got it! Page 75 of the current (0.04) draft of the Dart language spec has this note in it: Should we do something with respect to non-nullable types? If you asked me, I’d answer a resounding yes! (Alas, no one did, but that’s never stopped me before.) So, here’s my attempt at an an