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

[Copilot]

When a variant's stores are explicitly cleared (all removed), Pimcore's inheritance incorrectly pulls stores from the parent product. This happens because null (not set) and [] (explicitly empty) were treated identically.

Changes

• Multiselect::preGetData: Removed auto-conversion of null → [], preserving inheritance semantics
• Multiselect::isEmpty: Added override returning true only for null, not []
• Callers: Added ?? [] to 3 call sites (ProductController, CategoryController, ProductContext)

Semantics

// Before: Both null and [] triggered inheritance
$variant->setStores([]);  // Cleared → inherits from parent ❌

// After: Only null triggers inheritance  
$variant->setStores([]);  // Cleared → stays empty ✓
$variant->setStores(null); // Not set → inherits from parent ✓

Applies to all Multiselect-based fields (Stores, Countries, Currencies, Carriers, PaymentProviders).

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Differentiate between "empty" and "null" for "Stores" field</issue_title>
<issue_description>Hello,

as discussed per mail a few weeks ago:

For the "Stores" field, it would be nice to differentiate between "empty" and "null".

Right now, we have the following problem: If a variant has only one store assigned and that store gets removed, Pimcores inheritance kicks in and the variant inherits all stores from the parent product which is probably not the desired behavior in most cases.</issue_description>

Comments on the Issue (you are @copilot in this section)

@dpfaffenbauer but how? pimcore's inheritance works like that @dpfaffenbauer @YannicBoida Just trying to challenge ;)

• Fixes Differentiate between "empty" and "null" for "Stores" field #2918

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud