private String getServerUpdateRequest() {
        XMPPServer server = XMPPServer.getInstance();
        Element xmlRequest = docFactory.createDocument().addElement("version");
        // Add current openfire version
        Element openfire = xmlRequest.addElement("openfire");
        openfire.addAttribute("current", server.getServerInfo().getVersion().getVersionString());
        return xmlRequest.asXML();
    }
Returns the plugin update or {@code null} if the plugin is up to date.

@param pluginName     the name of the plugin (as described in the meta-data).
@param currentVersion current version of the plugin that is installed.
@return the plugin update or null if the plugin is up to date.
xmppserver/src/main/java/org/jivesoftware/openfire/update/UpdateManager.java