sku.php

<?php
 
namespace Bitrix\Catalog\Controller\Product;
 
use Bitrix\Catalog\ProductTable;
 
final class Sku extends Base
{
    protected const TYPE = ProductTable::TYPE_SKU;
    protected const LIST = 'UNITS';
 
    protected function getServiceListName(): string
    {
        return self::LIST;
    }
 
    protected function getAllowedProductTypes(): array
    {
        return [ProductTable::TYPE_SKU, ProductTable::TYPE_EMPTY_SKU];
    }
 
    public function addAction($fields): ?array
    {
        $fields['TYPE'] = ProductTable::TYPE_EMPTY_SKU;
        $result = parent::addAction($fields);
 
        return $this->fillKeyResponse($result);
    }
}