public function is_available_for_all() {
        if (is_null($this->availability)) {
            return true;
        } else {
            try {
                return $this->get_availability_tree()->is_available_for_all();
            } catch (\coding_exception $e) {
                $this->warn_about_invalid_availability($e);
                return false;
            }
        }
    }