code: public function next()
      {
          $this->currentChunk = $this->syncStorage->getChunk(1, $this->documentType, $this->shopId);
  
          if (empty($this->currentChunk)) {
              $this->valid = false;
  
              return;
          }
  
          $this->currentEntity = $this
              ->entityManager
              ->getRepository($this->entityClass)->find($this->currentChunk[0]['document_id']);
  
          if (!empty($this->currentEntity) || $this->currentChunk[0]['type'] == ActionTypes::DELETE) {
              $this->valid = true;
  
              return;
          }
  
          $this->valid = false;
      }
docs: {@inheritdoc}