diff --git a/src/WMS.Web.Api/Controllers/OutStockTaskController.cs b/src/WMS.Web.Api/Controllers/OutStockTaskController.cs
index 5007bfda..68f7c610 100644
--- a/src/WMS.Web.Api/Controllers/OutStockTaskController.cs
+++ b/src/WMS.Web.Api/Controllers/OutStockTaskController.cs
@@ -248,7 +248,10 @@ namespace WMS.Web.Api.Controllers
                 var slist = materialSubStocks.Where(t => t.MaterialNumber == x.MaterialNumber && t.StockCode == res.StockCode && t.OrgCode == res.OrgCode).Select(s => s.SubStock).ToList();
                 slist.ForEach(f => rList.Add(new GetOutStockTaskByNoSubStockResponse(f)));
                 x.MaterialSubStocks = rList.OrderBy(s => s.SubStock_Do).Select(s => s.SubStock).ToList();
-                x.FistSubStock = rList.OrderBy(s => s.SubStock_Do).First()?.SubStock_Do ?? "z";
+                if (rList.Count() > 0)
+                    x.FistSubStock = rList.OrderBy(s => s.SubStock_Do).First().SubStock_Do;
+                else
+                    x.FistSubStock = "z";
             });
             res.details = res.details.OrderBy(s => s.FistSubStock).ToList();