'Search function for message_follower_ids
Do not use with operator \'not in\'. Use instead message_is_followers'

@api.model
def _search_follower_partners(self, operator, operand):

    assert (operator != 'not    in'), "Do    not    search    message_follower_ids    with    'not    in'"
    followers = self.env['mail.followers'].sudo().search([('res_model', '=', self._name), ('partner_id', operator, operand)])
    return [('id', 'in', followers.mapped('res_id'))]
