missing currency in FIFO price_unit

account_thai.py
...
class purchase_order(osv.osv):
    _inherit="purchase.order"
...
def action_picking_create(self,cr,uid,ids,*args):
        pick_id=super(purchase_order,self).action_picking_create(cr,uid,ids,*args)
        pick=self.pool.get("stock.picking").browse(cr,uid,pick_id)
        for move in pick.move_lines:
            move.write({"price_unit": move.purchase_line_id.price_unit}) #missing currency!!!
        return pick_id