fix(*): IOrder.CustomerId nullable

Author: ddidgdimitrov-infragistics

NorthwindCRUD/Models/Contracts/IOrder.cs

@@ -7,7 +7,7 @@ public interface IOrder
     {
         int OrderId { get; set; }
 
-        string CustomerId { get; set; }
+        string? CustomerId { get; set; }
 
         int EmployeeId { get; set; }