code: public static Validator validCharset(String... charsets) {
      if (null == charsets || charsets.length == 0) {
        return new ValidCharset();
      } else {
        return new ValidCharset(charsets);
      }
    }
docs: Method will return a validator that will ensure that a String or List contains a charset that
  is supported by the system.
  
  @param charsets The charsets that are allowed. If empty all of the available charsets on the
  system will be included.
  @return validator