Non-declared variable in sale_stock.py gives error

Based on rev 9242,

sale_stock.py --> at the bottom end method _create_invoices(), I found that 2 variables are not declared, --> inv_amount and res.
In normal case, when sale.order_policy == 'picking', this method will not be used. So far, no problem.
Somehow, I write my own addons, which use this method on order_policy = picking, gives error (as variables are not declared).
May be the code need re-factoring??

================================

class sale_advance_payment_inv(osv.osv_memory):
    _inherit = "sale.advance.payment.inv"

    def _create_invoices(self, cr, uid, inv_values, sale_id, context=None):
        result = super(sale_advance_payment_inv, self)._create_invoices(cr, uid, inv_values, sale_id, context=context)
        sale_obj = self.pool.get('sale.order')
        sale_line_obj = self.pool.get('sale.order.line')
        wizard = self.browse(cr, uid, [result], context)
        sale = sale_obj.browse(cr, uid, sale_id, context=context)
        if sale.order_policy == 'postpaid':
            raise osv.except_osv(
                _('Error!'),
                _("You cannot make an advance on a sales order \
                     that is defined as 'Automatic Invoice after delivery'."))

        # kittiu: seem to be a bug as inv_amoutn is not declared. And in normal case, this part is not used, so I delete them.
# # If invoice on picking: add the cost on the SO
# # If not, the advance will be deduced when generating the final invoice
# line_name = inv_values.get('invoice_line') and inv_values.get('invoice_line')[0][2].get('name') or ''
# line_tax = inv_values.get('invoice_line') and inv_values.get('invoice_line')[0][2].get('invoice_line_tax_id') or False
# if sale.order_policy == 'picking':
# vals = {
# 'order_id': sale.id,
# 'name': line_name,
# 'price_unit': -inv_amount,
# 'product_uom_qty': wizard.qtty or 1.0,
# 'product_uos_qty': wizard.qtty or 1.0,
# 'product_uos': res.get('uos_id', False),
# 'product_uom': res.get('uom_id', False),
# 'product_id': wizard.product_id.id or False,
# 'discount': False,
# 'tax_id': line_tax,
# }
# sale_line_obj.create(cr, uid, vals, context=context)
        # -- kittiu:
        return result