Can't do a plain "return" in a Future<void> function (but can in Future<Null>)

[Hixie]

I believe the warning below is wrong.

import 'dart:async';

void foo1() {
  return;
}

Null foo2() {
  return;
}

Future<void> foo3() async {
  return; // warning • Missing return value after 'return' at test.dart:12:3 • return_without_value                                                                                                                                                            
}

Future<Null> foo4() async {
  return;
}

void main() { }

[matanlurey]

Duplicate of #32443.