diff --git a/product/ERP5/Document/TradeCondition.py b/product/ERP5/Document/TradeCondition.py
index 73d75638b6abb044340b5f7288129e334c3a3b4a..26c338a40cf1a4229f0d39a1f054cccaed3e86aa 100644
--- a/product/ERP5/Document/TradeCondition.py
+++ b/product/ERP5/Document/TradeCondition.py
@@ -152,7 +152,7 @@ class TradeCondition(Path, Transformation):
         for trade_model_line in specialise.contentValues(
             portal_type=self.model_line_portal_type_list):
           reference = trade_model_line.getReference()
-          if reference not in reference_list:
+          if reference not in reference_list or reference is None:
             trade_model_line_composed_list.append(trade_model_line)
             reference_list.append(reference)