@Nullable private static byte[] fromHex(String hex) throws DecoderException {
  return hex == null ? null : Hex.decodeHex(hex.toCharArray());
}

@ Nullable private static byte [ ] fromHex ( String hex ) throws DecoderException { return hex == null ? null : Hex . decodeHex ( hex . toCharArray ( ) ) ; }
covert hex to bytes
