public static Ip4Prefix valueOf(int address, int prefixLength) {
        return new Ip4Prefix(Ip4Address.valueOf(address), prefixLength);
    }
@Test(expected = IllegalArgumentException.class)
    public void testInvalidValueOfAddressNegativePrefixLengthIPv4() {
        Ip4Address ipAddress;
        Ip4Prefix ipPrefix;

        ipAddress = Ip4Address.valueOf("1.2.3.4");
        ipPrefix = Ip4Prefix.valueOf(ipAddress, -1);
    }