WP All import Woocommerce sale price

Hello i have problem with import my sale price.

In first step i have function for convert currency, etc.

<?php
function change_currency($price, $course=10) {
    return ($price/$course);
}
?>

And in wp all import field i have this code :

[change_currency({VARIANT[1]/PRICE_RETAIL[1]})]

But now i need update SALE price.

In my XML file the SALE PRICE value is not filled in all the time.
I need a solution for this , if there is a SALE price print it but before that I need the function to run CHANGE CURRENCY.

When i use this :

[change_currency({VARIANT[1]/PRICE_SALE[1]})]

all products that did not have a SALE price in the XML file got a price of 0 EUR.

Where am I going wrong? Thank you for your help.