pkg/front_end/testcases/general/null_aware_postfix.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
// @dart=2.9
class A {
  B b;
}

class B {
  C operator +(int i) => null;
}

class C extends B {}

main() {
  A a;
  a?.b++;
  C c = a?.b++;
}