关于 ASP.NET Web 应用中 async/await 注意问题

System.NullReferenceException: Object reference not set to an instance of an object.

at System.Web.ThreadContext.AssociateWithCurrentThread(System.Boolean setImpersonationContext) at offset 20
at System.Web.HttpApplication.OnThreadEnterPrivate(System.Boolean setImpersonationContext) at offset 12
at System.Web.HttpApplication.System.Web.Util.ISyncContext.Enter() at offset 0
at System.Web.Util.SynchronizationHelper.SafeWrapCallback(System.Action action) at offset 24
at System.Threading.Tasks.Task.Execute() at offset 16