'Overwrite the create method to add the user of groups'

@api.model
def create(self, vals):

    if vals.get('user_domain'):
        users = self._get_challenger_users(ustr(vals.get('user_domain')))
        if (not vals.get('user_ids')):
            vals['user_ids'] = []
        vals['user_ids'].extend(((4, user.id) for user in users))
    return super(Challenge, self).create(vals)
