public static IpAddress makeMaskPrefix(Version version, int prefixLength) {
        byte[] mask = makeMaskPrefixArray(version, prefixLength);
        return new IpAddress(version, mask);
    }
@Test(expected = IllegalArgumentException.class)
    public void testInvalidMakeNegativeMaskPrefixIPv6() {
        IpAddress ipAddress;

        ipAddress = IpAddress.makeMaskPrefix(IpAddress.Version.INET6, -1);
    }