public static IpPrefix valueOf(int address, int prefixLength) {
        return new IpPrefix(IpAddress.valueOf(address), prefixLength);
    }
@Test(expected = NullPointerException.class)
    public void testInvalidValueOfNullAddress() {
        IpAddress ipAddress;
        IpPrefix ipPrefix;

        ipAddress = null;
        ipPrefix = IpPrefix.valueOf(ipAddress, 24);
    }