@Nullable
  private static String decodeSeparator(String separator) {
    if (separator.length() % 6 != 0) {
      return null;
    }
    StringBuilder result = new StringBuilder();
    int pos = 0;
    while (pos < separator.length()) {
      String encodedCharacter = separator.substring(pos, pos+6);
      if (!encodedCharacter.startsWith("\\u")) {
        return null;
      }
      char code = (char) Integer.parseInt(encodedCharacter.substring(2), 16);
      result.append(code);
      pos += 6;
    }
    return result.toString();
  }
@Nullable
  private static String decodeSeparator(String separator)