Search a attribute in a xml document with java and XPath

i have the following method in java:

private static String getAttributValue(String attribute, String xmlResponseBody) {

    String searchAttributeValue = "";
    try {
        DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder docBuilder = docBuilderFactory.newDocumentBuilder();
        Document doc = docBuilder.parse(new InputSource(new StringReader(xmlResponseBody)));
        XPathFactory xPathFactory = XPathFactory.newInstance();
        XPath xpath = xPathFactory.newXPath();
        try {
            XPathExpression expr = xpath.compile("@" + attribute);
            Object result = expr.evaluate(doc, XPathConstants.NODESET);
            NodeList nodeList = (NodeList) result;
            Node node = nodeList.item(0);  // something wrong??
            searchAttributeValue = node.getTextContent();

        } catch (XPathExpressionException e) {
            e.printStackTrace();
        }
    } catch (ParserConfigurationException pce) {
        pce.printStackTrace();
    } catch (IOException ioe) {
        ioe.printStackTrace();
    } catch (SAXException sae) {
        sae.printStackTrace();
    }
    return searchAttributeValue;
}

I search an attribute (parameter "attribute") in a xml document (parameter "xmlResponseBody"). I would like to use XPath to solve this task. At the code, which i have comment with "// something wrong", the variable node is null. What should i do? What is the mistake in my code?

Thanks ! Marwief