#vulnerable code 
                             @Test
	public void writeXml_uri() {
		Attachment prop = new Attachment("image/png", "http://example.com/image.png");

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

		Document expected = xcalProperty(marshaller, "<uri>http://example.com/image.png</uri>");
		assertXMLEqual(expected, actual);
	} 
                            #location 6 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             @Test
	public void writeXml_uri() {
		Attachment prop = new Attachment("image/png", "http://example.com/image.png");
		assertWriteXml("<uri>http://example.com/image.png</uri>", prop, marshaller);
	}