/**
  * @return $this
  */
 public function addScheduleQuoteFilter()
 {
     $this->addFieldToFilter('status', array('in' => Adyen_Subscription_Model_Subscription::getScheduleQuoteStatuses()));
     $this->getSelect()->joinLeft(['subscription_quote' => $this->getTable('adyen_subscription/subscription_quote')], 'main_table.entity_id = subscription_quote.subscription_id AND subscription_quote.order_id IS NULL', []);
     $this->getSelect()->where('subscription_quote.entity_id IS NULL');
     return $this;
 }