@Override
    public int hashCode() {
      return 0;
    }
  }

  static class GoodNulls {
    public GoodNulls(String s) {
      checkNotNull(s);
    }

    public void rejectNull(String s) {
      checkNotNull(s);
    }
  }

  public static class BadNulls {
    public void failsToRejectNull(@SuppressWarnings("unused") String s) {}
  }