diff --git a/product/ERP5/Document/MirrorMovementGroup.py b/product/ERP5/Document/MirrorMovementGroup.py
index 12a0daa945533651cd5f61b6048739f28071e723..21bd85f7914739aa3a748cae3f60f224af68b3c4 100644
--- a/product/ERP5/Document/MirrorMovementGroup.py
+++ b/product/ERP5/Document/MirrorMovementGroup.py
@@ -51,6 +51,8 @@ class MirrorMovementGroup(MovementGroup):
   def _separate(self, movement_list):
     # record if mirrored or not in simulation movements.
     mapping_dict = {}
+    if len(movement_list) == 0:
+      return []
     for movement in movement_list:
       if _isMirrored(movement):
         applied_rule = movement.getParentValue()