$event parameter of EventManager::getListeners() mandatoryWhen calling EventManager::getListeners() you need to specify the event that
you want to fetch the listeners for. Call getAllListeners() instead if you
want to access the listeners of all events.
EventManager::getListeners() without an event nameWhen calling EventManager::getListeners() without an event name, all
listeners were returned, keyed by event name. A new method getAllListeners()
has been added to provide this functionality. It should be used instead.