public static byte[] hexString2Bytes(String hexString) {
        if (isSpace(hexString)) return null;
        int len = hexString.length();
        if (len % 2 != 0) {
            hexString = "0" + hexString;
            len = len + 1;
        }
        char[] hexBytes = hexString.toUpperCase().toCharArray();
        byte[] ret      = new byte[len >> 1];
        for (int i = 0; i < len; i += 2) {
            ret[i >> 1] = (byte) (hex2Dec(hexBytes[i]) << 4 | hex2Dec(hexBytes[i + 1]));
        }
        return ret;
    }
@Test
    public void hexString2Bytes() throws Exception {
        TestCase.assertTrue(
                Arrays.equals(
                        mBytes,
                        ConvertKit.hexString2Bytes(hexString)
                )
        );
    }