fix: Notice: Undefined offset: 0

src/QUI/ERP/Order/Mail.php

@@ -410,7 +410,7 @@ protected static function getOrderLocaleVar(OrderInterface $Order, $Customer): a
         if (empty($email)) {
             $mailList = $Address->getMailList();
 
-            if ($mailList[0]) {
+            if (isset($mailList[0])) {
                 $email = $mailList[0];
             }
         }