diff --git a/Myshipping.Application/Service/TaskManagePlat/TaskManageSISubmittedService.cs b/Myshipping.Application/Service/TaskManagePlat/TaskManageSISubmittedService.cs
index ab6a7ac0..1c489430 100644
--- a/Myshipping.Application/Service/TaskManagePlat/TaskManageSISubmittedService.cs
+++ b/Myshipping.Application/Service/TaskManagePlat/TaskManageSISubmittedService.cs
@@ -1511,8 +1511,25 @@ namespace Myshipping.Application
 
                             if (l.PropertyType == typeof(string))
                             {
-                                string st1 = (bkVal as string).AdjustString();
-                                string st2 = (siVal as string).AdjustString();
+                                string st1 = string.Empty;
+                                string st2 = string.Empty;
+
+                                if (bkVal == null)
+                                {
+                                    st1 = "";
+                                }
+                                else {
+                                    st1 = (bkVal as string).AdjustString();
+                                }
+
+                                if (siVal == null)
+                                {
+                                    st2 = "";
+                                }
+                                else
+                                {
+                                    st2 = (siVal as string).AdjustString();
+                                }
 
                                 if (!st1.Equals(st2))
                                 {