'Wrapper on message_subscribe, using users. If user_ids is not
provided, subscribe uid instead.'

@api.multi
def message_subscribe_users(self, user_ids=None, subtype_ids=None):

    if (user_ids is None):
        user_ids = [self._uid]
    return self.message_subscribe(self.env['res.users'].browse(user_ids).mapped('partner_id').ids, subtype_ids=subtype_ids)
