diff --git a/weboob/capabilities/base.py b/weboob/capabilities/base.py
index 68aa50f0d7f43f3844c320c47060a0d4766df73c..b6efc7687fae5cc72902d244dacfdd67fae82625 100644
--- a/weboob/capabilities/base.py
+++ b/weboob/capabilities/base.py
@@ -419,7 +419,7 @@ class Transfer(BaseObject):
     _fields = None
 
     def __init__(self, id=u'', url=NotLoaded, backend=None):
-        self.id = to_unicode(id)
+        self.id = to_unicode(id) if id is not None else u''
         self.backend = backend
         self._fields = deepcopy(self._fields)
         self.__setattr__('url', url)