@Override
    public XmlStringBuilder toXML(XmlEnvironment xmlEnvironment) {
        return new XmlStringBuilder(this).closeEmptyElement();
    }
@Test
    public void serializationTest() {
        RetractElement retractElement = new RetractElement();
        String expectedXml = "<retract xmlns='urn:xmpp:message-retract:0'/>";

        assertXmlSimilar(expectedXml, retractElement.toXML());
    }