public static Ip4Address makeMaskPrefix(int prefixLength) {
        byte[] mask = IpAddress.makeMaskPrefixArray(VERSION, prefixLength);
        return new Ip4Address(mask);
    }
@Test(expected = IllegalArgumentException.class)
    public void testInvalidMakeNegativeMaskPrefixIPv4() {
        Ip4Address ipAddress;

        ipAddress = Ip4Address.makeMaskPrefix(-1);
    }