public static boolean equals(@Nullable String s1, @Nullable String s2) {
    //noinspection StringEquality
    if (s1 == s2) return true;
    if (s1 == null || s2 == null) return false;

    if (s1.length() != s2.length()) return false;
    return s1.equals(s2);
  }
public static boolean equals(@Nullable String s1, @Nullable String s2)