error should be returned in todict

tiramisu/storage/sqlite3/storage.py

@@ -86,7 +86,7 @@ def delete_session(session_id,
     cursor.close()
 
 
-class Storage(object):
+class Storage:
     __slots__ = ('_conn', '_cursor', 'persistent', 'session_id', 'session_name', 'created')
     storage = 'sqlite3'
 

tiramisu/todict.py

@@ -873,7 +873,7 @@ class TiramisuDict:
                         else:
                             raise ValueError(_('only multi option can have action "add", but "{}" is not a multi').format(path))
                     else:
-                        raise ValueError(_('unknown action'))
+                        raise ValueError(_('unknown action {}').format(update['action']))
                 except ValueError as err:
                     updates_status.setdefault(path, {})[index] = [err]
             if warns != []:
@@ -897,7 +897,7 @@ class TiramisuDict:
             values = {'updates': list_keys(old_model, new_model, order, updates_status),
                       'model': new_model}
         else:
-            values = None
+            values = updates_status
         return values
 
     def todict(self,