diff --git a/CoviDok/BLL/PropertyCopier.cs b/CoviDok/BLL/PropertyCopier.cs
index 51020a7..d309141 100644
--- a/CoviDok/BLL/PropertyCopier.cs
+++ b/CoviDok/BLL/PropertyCopier.cs
@@ -10,7 +10,11 @@ namespace CoviDok.BLL
     {
         public static void Copy(T source, T dest, string[] except = null)
         {
-            List<string> forbidden = new List<string>(except);
+            List<string> forbidden = new List<string>();
+            if (except != null)
+            {
+                forbidden.AddRange(except);
+            }
             PropertyInfo[] properties = source.GetType().GetProperties();
             foreach (var property in properties)
             {