--- a/editors/ConfTreeNodeEditor.py	Tue Sep 10 23:23:45 2013 +0200
+++ b/editors/ConfTreeNodeEditor.py	Wed Sep 11 23:48:41 2013 +0200
@@ -496,6 +496,8 @@
     def GetChoiceCallBackFunction(self, choicectrl, path):
         def OnChoiceChanged(event):
             res = self.SetConfNodeParamsAttribute(path, choicectrl.GetStringSelection())
+            if res is None:
+                res = ""
             choicectrl.SetStringSelection(res)
             event.Skip()
         return OnChoiceChanged