check if the value is not None in _setItemIdList

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@2679 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/DeliveryLine.py

@@ -401,6 +401,8 @@ Une ligne tarifaire."""
         Computes total_quantity of all given items and stores this total_quantity
         in the quantity attribute of the cell
       """
+      if value is None:
+        return
       previous_item_list = self.getAggregateValueList()
       given_item_id_list = value
       item_object_list = []