diff --git a/res.py b/res.py
index 2a7a1ad683..6c8d574c8c 100644
--- a/res.py
+++ b/res.py
@@ -93,7 +93,7 @@ class User(metaclass=PoolMeta):
     @classmethod
     def default_companies(cls):
         company = Transaction().context.get('company')
-        return [company] if company else None
+        return [company] if company else []
 
     @classmethod
     def default_company(cls):