Update getUserByCustomerNumber references to getCustomerByIdOrCustomerNumber and enhance null-checking in requireSelected.

services/nginx/app/routes/vehiclesRoute.php

@@ -158,7 +158,7 @@ class vehiclesRoute
                         } else {
                             // Set the customer_id to the one from the request
                             $target_user = (new users_o());
-                            $target_user->getUserByCustomerNumber((int)self::getParameter('customer_id'));
+                            $target_user->getCustomerByIdOrCustomerNumber((int)self::getParameter('customer_id'));
                         }
                     }
                 }