/**
  * Returns true if current result set contains one hit
  *
  * @link http://php.net/manual/en/iterator.valid.php
  * @return boolean
  */
 public function valid()
 {
     return
         $this->_nextScrollId !== null
         && $this->_currentResultSet !== null
         && $this->_currentResultSet->count() > 0;
 }