If movement_list is empty, then return an empty list and prevent

raising exception when sorting.


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@26504 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/CausalityAssignmentMovementGroup.py

@@ -42,6 +42,8 @@ class CausalityAssignmentMovementGroup(MovementGroup):
     return self._addCausalityToEdit(movement)
 
   def _separate(self, movement_list):
+    if not movement_list:
+      return []
     property_dict = {}
     for movement in movement_list:
       self._addCausalityToEdit(movement, property_dict)