ETag已经设置 - 部分视图出错

Question

protected override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        base.OnActionExecuted(filterContext);
        AddRequiredInfoToViewBag();

        if (Request.IsAjaxRequest())
        {
            Response.CacheControl = "no-cache";
            Response.Cache.SetETag((Guid.NewGuid()).ToString());
        }
    }

当我从部分View调用动作时，上面的代码崩溃了。有人知道如何检查ETag是否已在缓存中设置？