/**
* Checks if the event has registered listeners.
* If the event has listeners this listeners will be executed with the given event arguments.
* The event arguments have to been an array or an instance of the Enlight_Event_EventArgs class.
* If the given arguments not an array or an instance of the Enlight_Event_EventArgs class enlight
* throw an Enlight_Event_Exception.
* Before the listener will be executed the the flag "processed" will be set to false in the event arguments.
* After all event listeners has been executed the "processed" flag will be set to true.
*
* The event listeners will be executed until one of the listeners return not null.
*
* @param string $event
* @param Enlight_Event_EventArgs|array|null $eventArgs
*
* @throws Enlight_Exception
*
* @return Enlight_Event_EventArgs|null
*/