protected function addDivider(ItemInterface $menu)
    {
        do {
            $name = 'divider'.mt_rand();
        } while (in_array($name, $this->dividers));

        $this->dividers[] = $name;

        $item = $menu->addChild($name, array());
        $item->setLabel('');
        $item->setAttribute('class', 'divider');

        return $item;
    }