throws Throwable
  public static String rtrim(Env env,                             String string,                             @Optional String characters)    throws Throwable  {    boolean []trim;    if (characters.equals(""))      trim = TRIM_WHITESPACE;    else      trim = parseCharsetBitmap(characters);    for (int i = string.length() - 1; i >= 0; i--) {      char ch = string.charAt(i);      if (ch >= 256 || ! trim[ch]) {        if (i == string.length())          return string;        else          return string.substring(0, i + 1);      }    }    return "";  }