/**
* Set the value in the event.
*
* @param GetGroupHeaderEvent $event The event being emitted.
*
* @param string $value The value returned by the callback.
*
* @return void
*/
public function update($event, $value)
{
if ($value === null) {
return;
}
$event->setValue($value);
$event->stopPropagation();
}
