* Load a list of database rows (numeric column indexing)
  * If <var>key</var> is not empty then the returned array is indexed by the value
  * the database key.  Returns <var>null</var> if the query fails.
  * @param  string  $key  The field name of a primary key
  * @return array         If <var>key</var> is empty as sequential list of returned records.
  * @throws  \RuntimeException
 public function loadRowList($key = null)
     $resultArray = $this->_db->loadRowList($key);
     return $this->_nullToArray($resultArray);