一个关于FileUpload控件上传图片的问题，求解答~

总是说image_url1不接受空值，我把非空属性改了之后错误时没了，但是数据表top_list_left里的image_url里 
根本没有东西啊，fileupload更本就没有上传成功，麻烦各位大大帮我解答下市为什么，谢谢 
protected void LinqDataSource1_Inserting(object sender, LinqDataSourceInsertEventArgs e) 
    { 
        Top_list_left uploadpic1 = (Top_list_left)e.NewObject; 
      // uploadpic1.Class_1 = Convert.ToString(Request.QueryString.Get("Class_1")); 
        FileUpload FileUpload1 = (FileUpload)ListView1.InsertItem.FindControl("FileUpload1"); 
        string virtualFolder = "~/BigPics/"; 
        string physicalFolder = Server.MapPath(virtualFolder); 
        string fileName = Guid.NewGuid().ToString(); 
        string extension = System.IO.Path.GetExtension(FileUpload1.FileName); 
        FileUpload1.SaveAs(System.IO.Path.Combine(physicalFolder,fileName+extension)); 
        uploadpic1.ImageUrl_1 = virtualFolder+fileName+extension; 
    } 
    protected void ListView1_ItemInserting(object sender, ListViewInsertEventArgs e) 
    { 
        FileUpload FileUpload1 = (FileUpload)ListView1.InsertItem.FindControl("FileUpload1"); 
        if (!FileUpload1.HasFile || !FileUpload1.FileName.ToLower().EndsWith(".jpg")) 
        { 
            CustomValidator CustomValidator1 = (CustomValidator)ListView1.InsertItem.FindControl("CustomValidator1"); 
            CustomValidator1.IsValid = false; 
            e.Cancel = true; 
        } 
    }