private function get_export_discussion_html() : ?string {
        global $CFG;

        require_once($CFG->libdir . '/portfoliolib.php');
        $discussion = $this->discussion;
        $button = new \portfolio_add_button();
        $button->set_callback_options('forum_portfolio_caller', ['discussionid' => $discussion->get_id()], 'mod_forum');
        $button = $button->to_html(PORTFOLIO_ADD_FULL_FORM, get_string('exportdiscussion', 'mod_forum'));
        return $button ?: null;
    }