UpdateItemResponse.ReturnedItem is null from Exchange Server

I am able to update the contacts, but I would like to know if with some contact happens a error, to know which ExchId happens the error, but ReturnedItem is null. is it possible to populate this info ?



 ServiceResponseCollection<UpdateItemResponse>  responses= service.UpdateItems(lstContacts, objContactSyncFolderID, ConflictResolutionMode.AlwaysOverwrite, null, null);

            var ltError = responses.Where(uiRes => uiRes.Result == ServiceResult.Error).ToList();


            foreach (var item in ltError)
            {
                string ExchId = item.ReturnedItem.Id.UniqueId; ///
            }