Error commit confmanager

Hello,

I want to use the commit method of ConfManager but I have this part of message :
...
 "/usr/lib/pymodules/python2.7/ajenti/plugins/recovery/api.py", line 104, in finished
    Manager(self.app).backup(cfg)
  File "/usr/lib/pymodules/python2.7/ajenti/plugins/recovery/api.py", line 67, in backup
    for f in provider.list_files():
AttributeError: 'NoneType' object has no attribute 'list_files'

But I have this method in my class. And I read this doc : http://wiki.ajenti.org/tutorial:tutorial

Thank you