如何解决global.aspx中Log.Error（ex）中的NullReferenceException异常

Question

我的C＃代码就像这样

    protected void Application_Error(object sender, EventArgs e)
    {
        var ex = Server.GetLastError();
        Log.Error(ex);
        var httpStatusCode = (ex is HttpException) ? (ex as HttpException).GetHttpCode() : 500;

        var httpContext = ((MvcApplication)sender).Context;
        httpContext.ClearError();
        httpContext.Response.Clear();
        httpContext.Response.StatusCode = httpStatusCode;

        var shouldHandleException = true;
        Exception exceptionToReplace;         
    }

Log.Error（ex）; 抛出此 System.NullReferenceException：对象引用未设置为对象实例错误导致var ex = 服务器.GetLastError（）; 为空。我的问题是如何解决这个错误？任何信息都会对此有所帮助