Send an empty history if nothing is found.

git-svn-id: https://svn.erp5.org/repos/neo/branches/prototype3@210 71dcc9de-d417-0410-9af5-da40c76e7ee4

neo/storage/operation.py

@@ -345,6 +345,8 @@ class OperationEventHandler(StorageEventHandler):
 
         app = self.app
         history_list = app.dm.getObjectHistory(oid, first, last - first)
+        if history_list is None:
+            history_list = []
         conn.addPacket(Packet().answerObjectHistory(packet.getId(), oid,
                                                     history_list))