_fetch404(path, qs, cb = noop) {
      const { loadSidebar, requestHeaders, notFoundPage } = this.config;

      const fnLoadSideAndNav = this._loadSideAndNav(path, qs, loadSidebar, cb);
      if (notFoundPage) {
        const path404 = this.#get404Path(path, this.config);

        this.#request(this.router.getFile(path404), requestHeaders).then(
          (text, opt) => this._renderMain(text, opt, fnLoadSideAndNav),
          _error => this._renderMain(null, {}, fnLoadSideAndNav),
        );
        return true;
      }

      this._renderMain(null, {}, fnLoadSideAndNav);
      return false;
    }
Load the 404 page
@param {String} path URL to be loaded
@param {*} qs TODO: define
@param {Function} cb Callback
@returns {Boolean} True if the requested page is not found
@private