public function setPropertyList(Erfurt_Sparql_Query2_PropertyList $propertyList)
 {
     if ($propertyList->isEmpty()) {
         throw new RuntimeException('Argument 1 passed to Erfurt_Sparql_Query2_BlankNodePropertyList::setPropertyList must not be an empty PropertyList', E_USER_ERROR);
     }
     $this->propertyList = $propertyList;
 }