diff --git a/Gatedge.K3.Pilot.PlugIn/BOSPlugIn/Sal_Order/Bill.cs b/Gatedge.K3.Pilot.PlugIn/BOSPlugIn/Sal_Order/Bill.cs
index d45e3a3..62ee971 100644
--- a/Gatedge.K3.Pilot.PlugIn/BOSPlugIn/Sal_Order/Bill.cs
+++ b/Gatedge.K3.Pilot.PlugIn/BOSPlugIn/Sal_Order/Bill.cs
@@ -90,7 +90,7 @@ namespace Gatedge.K3.Pilot.PlugIn.BOSPlugIn.Sal_Order
                             this.Model.SetValue("F_AGREEPRICE", F_AGREEPRICE, rowIndex);
 
                             var custId = this.View.Model.GetValue("FCustID") as DynamicObject;
-                            var creditClassificationId = custId["F_CreditClassification_Id"];
+                            var creditClassificationId = custId["F_CreditClassification_Id"]?.ToString();
                             if (!creditClassificationId.IsNullOrEmptyOrWhiteSpace())
                             {
                                 var creditClassification = custId["F_CreditClassification"] as DynamicObject;