protected function get_slots_in_request($postdata = null) {
        // Note: we must not use "question_attempt::get_submitted_var()" because there is no attempt instance!!!
        if (is_null($postdata)) {
            $slots = optional_param('slots', null, PARAM_SEQUENCE);
        } else if (array_key_exists('slots', $postdata)) {
            $slots = clean_param($postdata['slots'], PARAM_SEQUENCE);
        } else {
            $slots = null;
        }
        if (is_null($slots)) {
            $slots = $this->get_slots();
        } else if (!$slots) {
            $slots = array();
        } else {
            $slots = explode(',', $slots);
        }
        return $slots;
    }