Do not get stat_method if stat_method_id is None.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@22141 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Form/ListBox.py

@@ -1910,7 +1910,7 @@ class ListBoxRendererLine:
           # If a stat method is not specified, use the result in the context itself.
           original_value = getattr(context, alias)
           processed_value = original_value
-        else:
+        elif stat_method_id is not None:
           stat_method = getattr(context, stat_method_id)
           if callable(stat_method):
             try: