/**
  * Loads one page of resource into iterator.
  */
 private function load()
 {
     if ($this->pageIterator === NULL || !$this->pageIterator->valid()) {
         $this->pageIterator = new IteratorIterator($this->resourceLoader->getNextPage());
         $this->pageIterator->rewind();
         if (!$this->pageIterator->valid()) {
             $this->counter = NULL;
         }
     }
 }