public function onNavigationItemChildrenRequested(NavigationItem $oNavigationItem)
 {
     $mIdentifier = $oNavigationItem->getIdentifier();
     if ($oNavigationItem instanceof PageNavigationItem && $oNavigationItem->getMe()->isOfType('journal')) {
         $this->addChildrenToPageNavigationItem($oNavigationItem);
     } else {
         if ($oNavigationItem instanceof VirtualNavigationItem) {
             $this->addChildrenToVirtualNavigationItem($oNavigationItem);
         }
     }
 }