BackgroundWorker结果正在被清除

Question

在我的代码中，我使用后台工作程序来执行任务，并将该任务的返回值设置为DoWorkEventArgs结果。奇怪的是，在DoWork事件期间，Result已设置并包含项目，但是当我在RunWorkerCompleted事件中访问结果时，SOMETIMES结果为空！

        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            var i =  YouTubeDownloader.GetYouTubeVideoUrls(videoUrls);
            e.Result = i; //Contains items
        }

        private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
                UseWaitCursor = false;
                if (e.Error != null)
                    throw e.Error;

                List<YouTubeVideoQuality> urls = e.Result as List<YouTubeVideoQuality>; // Empty?