[Zope] about the IMAPAdapter Product product

The lines 106-108 of the file "IMAPAdapter.py" are: def addIMAPAdapter(self, title='', default_domain='', smtp_server='', smtp_port=25, imap_server='', imap_port=143, roles, REQUEST=None): the roles parameter has no default value while REQUEST has, this gives me an error. Shouldn't it be roles=''? And a question, the method validate begins: def validate(self, request, auth='', roles=None): """ """ if 'NotMail' not in roles: <--- Why these two lines? return None <--- Thanks for your time, David