public static byte[] fromHexString(final String values) {
        return fromHexString(values, ":");
    }
@Test(expected = NumberFormatException.class)
    public void testFromHexStringError() {
        String invalidStr = "00:00:00:00:00:00:ffff";
        HexString.fromHexString(invalidStr);
        fail("HexString.fromHexString() should have thrown a NumberFormatException");
    }