public static Ip6Prefix valueOf(byte[] address, int prefixLength) {
        return new Ip6Prefix(Ip6Address.valueOf(address), prefixLength);
    }
@Test(expected = IllegalArgumentException.class)
    public void testInvalidValueOfAddressNegativePrefixLengthIPv6() {
        Ip6Address ipAddress;
        Ip6Prefix ipPrefix;

        ipAddress =
            Ip6Address.valueOf("1111:2222:3333:4444:5555:6666:7777:8888");
        ipPrefix = Ip6Prefix.valueOf(ipAddress, -1);
    }