/**
     * Get the URL for the previous request.
     *
     * @param  mixed  $fallback
     * @return string
     */
    public function previous($fallback = false)
    {
        $referrer = $this->request->headers->get('referer');

        $url = $referrer ? $this->to($referrer) : $this->getPreviousUrlFromSession();

        if ($url) {
            return $url;
        } elseif ($fallback) {
            return $this->to($fallback);
        }

        return $this->to('/');
    }