public static Ip6Address makeMaskPrefix(int prefixLength) {
        byte[] mask = IpAddress.makeMaskPrefixArray(VERSION, prefixLength);
        return new Ip6Address(mask);
    }
@Test(expected = IllegalArgumentException.class)
    public void testInvalidMakeTooLongMaskPrefixIPv6() {
        Ip6Address ipAddress;

        ipAddress = Ip6Address.makeMaskPrefix(129);
    }