Wrong XML structure XML. Parsing – android

I'm trying to parse this link.

This is my DocumentBuilder:

public final static Document XMLfromString(String xml) {
    Document doc = null;

    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
    try {

        DocumentBuilder db = dbf.newDocumentBuilder();

        InputSource is = new InputSource();
        is.setCharacterStream(new StringReader(xml));
        doc = db.parse(is);

    } catch (ParserConfigurationException e) {
        System.out.println("XML parse error: " + e.getMessage());
        return null;
    } catch (SAXException e) {
        System.out.println("Wrong XML file structure: " + e.getMessage());
        return null;
    } catch (IOException e) {
        System.out.println("I/O exeption: " + e.getMessage());
        return null;
    }

    return doc;
}

Every time I get "NullPointerException: Attempt to invoke interface method 'org.w3c.dom.Element org.w3c.dom.Document.getDocumentElement()' on a null object reference" when I try to get NodeList nl = doc.getElementsByTagName("item"); because of Wrong XML file structure.