in stock.picking, i added a new one2many field for printing

class incomingShipments_picking(osv.osv):

    _inherit = 'stock.picking.in'
    
    _columns = {
        'summary_lines': fields.one2many('stock.move.summary', 'picking_id', 'Summary'),
    }
incomingShipments_picking();

class incomingshipments_summary(osv.osv):

    _name = 'stock.move.summary'
    
    _columns = {
        'product_id': fields.many2one('product.product', 'Product'),
        'picking_id': fields.many2one('stock.picking', 'Reference'),
        'qty': fields.integer('Quantity'),
        'state': fields.selection(
        [('draft', 'Draft'),
        ('auto', 'Waiting Another Operation'),
        ('confirmed', 'Waiting Availability'),
        ('assigned', 'Inbound'),
        ('delivered', 'Delivered'),
        ('done', 'Received'),
        ('cancel', 'Cancelled'),],
        'Status', select=True),
        'date': fields.datetime('Date', select=True, states={'done': [('readonly', True)]}),

    }
incomingshipments_summary();

and i added a section in my rml file:

<section>
        <para style="P1">[[repeatIn(o.summary_lines,'l')]]</para>
        <blockTable colWidths="280,255" style="Table_Order_Pur_line_Content">
        <tr>
            <td>
                <para style="P1">[[l.product_id.name]]</para>
            </td>
            <td>
                <para style="P1">[[l.qty]]</para>
            </td>
        </tr>
      </blockTable>
    </section>

and it shows error

except_osv: (u'summary_lines', (<type 'exceptions.AttributeError'>, AttributeError(KeyError('summary_lines',),), <traceback object at 0x7ff9fbd47ef0>))

What should I do to solve this problem?