public static boolean containsOnlyWhiteSpaces(@Nullable CharSequence chars) {
    if (chars == null) return true;
    for (int i = 0; i < chars.length(); i++) {
      char c = chars.charAt(i);
      if (c == ' ' || c == '\t' || c == '\n' || c == '\r') continue;
      return false;
    }
    return true;
  }
public static boolean containsOnlyWhiteSpaces(@Nullable CharSequence chars)