#vulnerable code 
                             @Test
	public void writeXml() {
		IntegerProperty prop = new IntegerProperty(5);

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

		Document expected = xcalProperty(marshaller, "<integer>5</integer>");
		assertXMLEqual(expected, actual);
	} 
                            #location 6 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             @Test
	public void writeXml() {
		IntegerProperty prop = new IntegerProperty(5);
		assertWriteXml("<integer>5</integer>", prop, marshaller);
	}