class Class {
  A nonNullableField = const A();
  A get nonNullableProperty => nonNullableField;
  void set nonNullableProperty(A value) {}
  A nonNullableMethod() => nonNullableField;
}

class A {
  const A();
  A get nonNullableProperty => this;
}

main() {}
expect(expected, actual) {}
throws(void Function() f) {}