Fix PHP 8.5 ErrorException when creating a new product (null getById)

[rhoerr]

Summary

Fixes mage-os/mageos-magento2#289 — creating a new product in the admin throws an ErrorException under PHP 8.5:

Using null as an array offset is deprecated, use an empty string instead

Root cause

The stack trace lands in Magento\Catalog\Model\ProductRepository::getById(), but the null originates in this module's product-form modifier:

TranslationStores::modifyMeta → customizeTranslationStoresList → getTranslationStores() called:

$this->productRepository->getById($this->request->getParam("id"));

On the Add Product form there is no id request param, so getParam("id") returns null. getById(null) then uses null as an array offset internally ($this->instancesById[null][...]), which is a deprecation-turned-ErrorException in developer mode on PHP 8.5. The surrounding try/catch only caught NoSuchEntityException, so it escaped.

Fix

Return early when there is no product id (a new product has no assigned stores to translate), and cast the id to int for the load. This mirrors the guard the module already uses for the CMS-block button (!getParam('block_id')), which is why that path was never affected.

$productId = $this->request->getParam("id");
if (empty($productId)) {
    return $translationStores;
}
$currentProduct = $this->productRepository->getById((int)$productId);

Tests

Adds Test/Unit/.../TranslationStoresTest.php:

• getById() is never called for a new product (no id param)
• getById() is called with the id cast to int for an existing product

Verified the test fails with the fix reverted and passes with it.

Notes

• Backward compatible; no API/schema changes.
• CHANGELOG updated ([2.1.3]).

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