SharePoint API ClientContextLoad属性未初始化

我有以下代码(SharePointUpload是一个自定义类，我有一个包含Microsoft.SharePoint.Client.File对象):

private static bool LoadSharePointFile(SharePointUpload fileUpload)
{
    ClientContext clientContext = HttpContextManager.SharepointClientContext;
    Microsoft.SharePoint.Client.File file = clientContext.Web.GetFileByServerRelativeUrl(fileUpload.FullSharepointPath);
    clientContext.Load(file, f => f.CheckOutType, f => f.MajorVersion);
    clientContext.ExecuteQuery();
    fileUpload.File = file;
}

在这个方法返回之后，我立即像下面这样访问CheckOutType属性:

if (fileUpload.File.CheckOutType != CheckOutType.None)
{
  ...
}

我得到这个错误:

Microsoft.SharePoint.Client.PropertyOrFieldNotInitializedException:属性或字段尚未初始化。它还没有已请求或请求尚未执行。它可能需要这样做显式地请求。在Microsoft.SharePoint.Client.ClientObject.CheckUninitializedProperty(字符串propName)

为什么我得到这个错误?这个属性不是像我在context的Load方法中定义的那样初始化了吗?

using (ClientContext ctx = ....))
{
    Web web = ctx.Web;
    ctx.Load(web);
    ctx.ExecuteQuery();

    Microsoft.SharePoint.Client.File file = web.GetFileByServerRelativeUrl(fileUpload.FullSharepointPath);
clientContext.Load(file, f => f.CheckOutType, f => f.MajorVersion);
clientContext.ExecuteQuery();
}