#vulnerable code 
                             @Test
	public void writeXml() {
		Geo prop = new Geo(12.34, 56.78);

		Document actual = xcalProperty(marshaller);
		marshaller.writeXml(prop, XmlUtils.getRootElement(actual));

		Document expected = xcalProperty(marshaller, "<latitude>12.34</latitude><longitude>56.78</longitude>");
		assertXMLEqual(expected, actual);
	} 
                            #location 6 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             @Test
	public void writeXml() {
		Geo prop = new Geo(12.34, 56.78);
		assertWriteXml("<latitude>12.34</latitude><longitude>56.78</longitude>", prop, marshaller);
	}