/**
  * Callback listener for get node items.
  *
  * @return null|string
  */
 public function getItems()
 {
     if ($this->node['type'] !== 'regular') {
         return null;
     }
     $dataProvider = new DefaultDataProvider();
     $dataProvider->setBaseConfig(array('source' => 'tl_article'));
     $count = $dataProvider->getCount($dataProvider->getEmptyConfig()->setFilter(array(array('property' => 'pid', 'value' => $this->node['id'], 'operation' => '='))));
     if (intval($count) <= 0) {
         return null;
     }
     return $this->getArticleNode($this->node['id']);
 }
 /**
  * check if calendar is empty.
  *
  * @param $node
  *
  * @return bool
  */
 protected function isEmptyCalendar($node)
 {
     $dataProvider = new DefaultDataProvider();
     $dataProvider->setBaseConfig(array('source' => 'tl_calendar_events'));
     $count = $dataProvider->getCount($dataProvider->getEmptyConfig()->setFilter(array(array('property' => 'pid', 'value' => $node['id'], 'operation' => '='))));
     if (intval($count) <= 0) {
         return true;
     }
     return false;
 }