@classmethod
def preprocess(cls, data):
    """
        A preprocessor for the order form data that can be overridden
        by custom form classes. The default preprocessor here handles
        copying billing fields to shipping fields if "same" checked.
        """
    if data.get('same_billing_shipping', '') == 'on':
        for field in data:
            bill_field = field.replace('shipping_detail', 'billing_detail')
            if field.startswith('shipping_detail') and bill_field in data:
                data[field] = data[bill_field]
    return data
