docs: def handle_not_found(exception, **extra):
      """Custom blueprint exception handler."""
      assert isinstance(exception, NotFound)
  
      page = Page.query.filter(db.or_(Page.url == request.path,
                                      Page.url == request.path + "/")).first()
  
      if page:
          _add_url_rule(page.url)
          return render_template(
              [
                  page.template_name,
                  current_app.config['PAGES_DEFAULT_TEMPLATE']
              ],
              page=page
          )
      elif 'wrapped' in extra:
          return extra['wrapped'](exception)
      else:
          return exception