/**
  * Property isset access.
  * 
  * @param string $propertyName Name of the property.
  * @return bool True is the property is set, otherwise false.
  * @ignore
  */
 public function __isset($propertyName)
 {
     if (array_key_exists($propertyName, $this->properties)) {
         return true;
     }
     return parent::__isset($propertyName);
 }