Differentiate between null and empty array for Stores field to prevent unwanted inheritance

src/CoreShop/Behat/Context/Setup/ProductContext.php

@@ -118,7 +118,7 @@ public function theSiteHasAProductPricedAt(string $productName, int $price = 100
      */
     public function theProductIsPriced(ProductInterface $product, int $price, StoreInterface $store): void
     {
-        $product->setStores(array_merge($product->getStores(), [$store->getId()]));
+        $product->setStores(array_merge($product->getStores() ?? [], [$store->getId()]));
         $product->setStoreValuesOfType('price', $price, $store);
 
         $this->saveProduct($product);

src/CoreShop/Bundle/FrontendBundle/Controller/CategoryController.php

@@ -258,9 +258,9 @@ protected function validateCategory(Request $request, CategoryInterface $categor
             throw new NotFoundHttpException('category not found');
         }
 
-        if (!in_array($this->getContext()->getStore()->getId(), array_values($category->getStores()))) {
+        if (!in_array($this->getContext()->getStore()->getId(), array_values($category->getStores() ?? []))) {
             throw new NotFoundHttpException(
-                sprintf(sprintf('store (id %s) not available in category', $this->getContext()->getStore()->getId())),
+                sprintf('store (id %s) not available in category', $this->getContext()->getStore()->getId()),
             );
         }
     }

src/CoreShop/Bundle/FrontendBundle/Controller/ProductController.php

@@ -82,7 +82,7 @@ protected function validateProduct(Request $request, ProductInterface $product):
             throw new NotFoundHttpException('product not found');
         }
 
-        if (!in_array($this->container->get(StoreContextInterface::class)->getStore()->getId(), $product->getStores())) {
+        if (!in_array($this->container->get(StoreContextInterface::class)->getStore()->getId(), $product->getStores() ?? [])) {
             throw new NotFoundHttpException('product not found');
         }
     }

src/CoreShop/Bundle/ResourceBundle/CoreExtension/Multiselect.php

@@ -48,10 +48,24 @@ public function preGetData($object, $params = [])
 
         $data = $object->getObjectVar($this->getName());
 
-        if (null === $data) {
-            $data = [];
-        }
-
+        // Don't convert null to empty array to allow Pimcore's inheritance to work
+        // null means "not set" and will inherit from parent
+        // empty array means "explicitly set to no values" and won't inherit
         return $data;
     }
+
+    /**
+     * Checks if data is empty. Returns true only for null, not for empty arrays.
+     * This allows differentiating between "not set" (null) and "explicitly empty" ([]).
+     *
+     * @param array|null $data
+     *
+     * @return bool
+     */
+    public function isEmpty($data): bool
+    {
+        // Only null is considered empty (will inherit from parent)
+        // Empty array [] is NOT empty (explicitly set to no values, won't inherit)
+        return null === $data;
+    }
 }