@Contract(value = "null,!null -> false; !null,null -> false; null,null -> true", pure = true)
  public static boolean equal(CharSequence s1, CharSequence s2) {
    return StringUtilRt.equal(s1, s2, true);
  }
@Contract(value = "null,!null -> false; !null,null -> false; null,null -> true", pure = true)
  public static boolean equal(CharSequence s1, CharSequence s2)