public function notify(string $event, array $arguments = null)
    {
        if (isset($this->events[$event])) {
            foreach ($this->events[$event] as $priorityKey => $callbackKey) {
                $output = $this->subscriptions[$callbackKey]($this, $arguments ?? []);
                if (isset($output['stop']) && true === $output['stop']) {
                    break;
                }
            }
        }
    }