/**
  * @param  CallbackBag $callbackBag
  * @return mixed
  */
 public function callback(CallbackBag $callbackBag)
 {
     if (count($callbackBag->getArguments()) !== 0) {
         throw new \InvalidArgumentException($this->getPrefix() . ' accessor allows no argument!');
     }
     return $callbackBag->getProperty();
 }