protected function notify_graders(stdClass $submission) {
        global $DB, $USER;

        $instance = $this->get_instance();

        $late = $instance->duedate && ($instance->duedate < time());

        if (!$instance->sendnotifications && !($late && $instance->sendlatenotifications)) {
            // No need to do anything.
            return;
        }

        if ($submission->userid) {
            $user = $DB->get_record('user', array('id'=>$submission->userid), '*', MUST_EXIST);
        } else {
            $user = $USER;
        }

        if ($notifyusers = $this->get_notifiable_users($user->id)) {
            foreach ($notifyusers as $notifyuser) {
                $this->send_notification($user,
                                         $notifyuser,
                                         'gradersubmissionupdated',
                                         'assign_notification',
                                         $submission->timemodified);
            }
        }
    }