class A {
  int? foo;
  A bar;
  A(this.bar);
}

test<T extends A?>(A? a, T t, dynamic d, int x) {}

class B {}

extension Extension on B {
  int? get fooExtension => null;
  void set fooExtension(int? value) {}
  B get barExtension => new B();
}

testExtension<T extends B?>(B? b, T t, int x) {}
main() {}