@Override
  public int compare(String s1, String s2) {
    //noinspection StringEquality
    if (s1 == s2) return 0;
    if (s1 == null) return -1;
    if (s2 == null) return +1;
    return naturalCompare(s1, s2, s1.length(), s2.length(), true, false);
  }
@Override
  public int compare(String s1, String s2)