HTML_Menu throwing notices

Hi, Just trying to get the example at http://pear.php.net/manual/en/package.html.html-menu.intro.php to work. It does work but also throws me a notice: Notice: Undefined index: in /usr/local/share/php/pear/HTML/Menu.php on line 462 I guess there's some array key missing but I cannot spot it.. Here's the code: <?php // Load the class require_once 'HTML/Menu.php'; $data = array( 1 => array(

       'title' => 'Menu item 1',
       'url' => '/item1.php',
       'sub' => array(
           11 => array('title' => 'Menu item 1.1', 'url' => '/item1.1.php'),
           12 => array(
               'title' => 'Menu item 1.2',
               'url' => '/item1.2.php',
               'sub' => array(
                   121 => array('title' => 'Menu item 1.2.1', 'url' => '/item1.2.1.php'),
                   122 => array('title' => 'Menu item 1.2.2', 'url' => '/item1.2.2.php')
               )
           )
       )

), 2 => array(

       'title' => 'Menu item 2',
       'url' => '/item2.php',
       'sub' => array(
           21 => array('title' => 'Menu item 2.1', 'url' => '/item2.1.php'),
           22 => array('title' => 'Menu item 2.2', 'url' => '/item2.2.php')
       )

) ); // Instantiate the menu object, we presume that $data contains menu structure $menu =& new HTML_Menu($data, 'sitemap'); // Output the menu $menu->show(); ?>