i'm doing searching and display customer name from stock.picking for custom module.

    stock_picking_id = fields.Many2one('stock.picking', string='Delivery Order', ondelete='restrict', required=True)
    stock_picking_customer = fields.Char(readonly=True, store=False, string='Customer')

    def stock_picking_id_change(self, cr, uid, ids, stock_picking_id, context=None):
        if stock_picking_id:
            stock_picking_obj = self.pool.get('stock.picking') 
            x = stock_picking_obj.browse(cr, uid, stock_picking_id, context=context)[0]
            return {'value': {'stock_picking_customer': x.partner_id}}
        return {'value': {}}

the return value are: res.partner(9,)

XML view:

                            <page string="Picking Lines">
                                <field name="order_line">
                                    <tree editable="bottom">
                                        <field name="stock_picking_id" string="Picking Number" on_change="stock_picking_id_change(stock_picking_id)"/>
                                        <field name="stock_picking_customer" string="Customer"/>
                                    </tree>
                                </field>
                            </page>

How are the correct syntax? The return value should be customer name.

Thanks