protected function getUsersToPullFor($notifiable)
    {
        foreach ($notifiable as $key => $toBeNotified) {
            if ( ! $toBeNotified instanceof Notifiable && ! $toBeNotified instanceof NotifiableGroup) {
                throw new NotNotifiableException("The members passed to the pull must implement the notifiable interface");
            }

            if ($toBeNotified instanceof NotifiableGroup) {
                $group = $toBeNotified->getGroup();

                if ($group instanceof Collection) {
                    $group = $group->all();
                }

                $notifiable = array_merge($notifiable, $group);

                unset($notifiable[$key]);
            }
        }

        return $notifiable;
    }