diff --git a/registration/model/__init__.py b/registration/model/__init__.py
index 2fd62ae..ab1f7ad 100644
--- a/registration/model/__init__.py
+++ b/registration/model/__init__.py
@@ -2,6 +2,8 @@
 from tg import config
 from tgext.pluggable import PluggableSession
 
+__all__ = ["Registration"]
+
 DBSession = PluggableSession()
 
 Registration = None
diff --git a/registration/model/ming_models.py b/registration/model/ming_models.py
index 26c6f3e..f7d0275 100644
--- a/registration/model/ming_models.py
+++ b/registration/model/ming_models.py
@@ -29,7 +29,7 @@ class __mongometa__:
     password = FieldProperty(s.String, required=True)
     code = FieldProperty(s.String)
     activated = FieldProperty(s.DateTime)
-    extras = FieldProperty(s.Anything)
+    extras = FieldProperty(s.Anything, if_missing=None)
 
     user_id = ForeignIdProperty(app_model.User)