public static Ip4Address valueOf(int value) {
        byte[] bytes =
            ByteBuffer.allocate(INET_BYTE_LENGTH).putInt(value).array();
        return new Ip4Address(bytes);
    }
@Test(expected = NullPointerException.class)
    public void testInvalidValueOfNullString() {
        Ip4Address ipAddress;

        String fromString = null;
        ipAddress = Ip4Address.valueOf(fromString);
    }