/**
  * @param Shift $shift
  * @param $driverId
  * @return null|DrivingAssertion
  */
 private function getDrivingAssertion(Shift $shift, $driverId)
 {
     /** @var DrivingAssertion $drivingAssertion */
     foreach ($shift->getDrivingAssertionsAsArray() as $drivingAssertion) {
         if ($drivingAssertion->getDriver()->getId() == $driverId) {
             return $drivingAssertion;
         }
     }
     return null;
 }