void_checks false positive with FutureOr<void> and NNBD

[a14n]

// @dart = 2.9
import 'dart:async';

void m(FutureOr<void> Function() f) {}

void main() {
  m(() {}); // void_checks false positive
}

[natebosch]

Here is another example that is easy to hit with unawaited from package:pedantic (at least until googlearchive/pedantic#69 goes in)

void main() {
  unawaited(Future.value(1).then((_) {})); // Error on argument to then
}

void unawaited(Future<void> f) {}