diff --git a/CHANGELOG-WIP.md b/CHANGELOG-WIP.md
new file mode 100644
index 0000000000..eaba982a22
--- /dev/null
+++ b/CHANGELOG-WIP.md
@@ -0,0 +1,11 @@
+# WIP Release Notes for Craft Commerce
+
+### Store Management
+
+### Administration
+
+### Development
+
+### Extensibility
+
+### System
\ No newline at end of file
diff --git a/CHANGELOG.md b/CHANGELOG.md
index eb5c08f57f..0d00136ad2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## Unreleased
 
 - Fixed a bug where catalog pricing rules could generate promotional prices for non-promotable purchasables. ([#4118](https://github.com/craftcms/commerce/issues/4118))
+- Fixed a bug where variants weren’t duplicating correctly. ([#4125](https://github.com/craftcms/commerce/issues/4125))
 - Fixed a SQL error that could occur when deleting a shipping method.
 
 ## 5.4.6 - 2025-09-04
diff --git a/src/base/Purchasable.php b/src/base/Purchasable.php
index d1d8fa70b9..889ec54c6a 100644
--- a/src/base/Purchasable.php
+++ b/src/base/Purchasable.php
@@ -683,7 +683,7 @@ public function getSkuAsText(): string
     /**
      * @param string|null $sku
      */
-    public function setSku(string $sku = null): void
+    public function setSku(?string $sku = null): void
     {
         $this->_sku = $sku;
     }
diff --git a/src/base/Stat.php b/src/base/Stat.php
index 6bc71ea77a..c3729bb3ed 100644
--- a/src/base/Stat.php
+++ b/src/base/Stat.php
@@ -41,7 +41,7 @@ abstract class Stat implements StatInterface, HasStoreInterface
      * @param DateTime|bool|null $endDate
      * @throws \Exception
      */
-    public function __construct(string $dateRange = null, mixed $startDate = null, mixed $endDate = null, ?int $storeId = null)
+    public function __construct(?string $dateRange = null, mixed $startDate = null, mixed $endDate = null, ?int $storeId = null)
     {
         $user = Craft::$app->getUser()->getIdentity();
         if ($user) {
diff --git a/src/controllers/CatalogPricingRulesController.php b/src/controllers/CatalogPricingRulesController.php
index 1d5fe92442..94adad958e 100755
--- a/src/controllers/CatalogPricingRulesController.php
+++ b/src/controllers/CatalogPricingRulesController.php
@@ -73,7 +73,7 @@ public function actionIndex(?string $storeHandle = null): Response
      * @throws HttpException
      * @throws InvalidConfigException
      */
-    public function actionEdit(?string $storeHandle = null, int $id = null, CatalogPricingRule $catalogPricingRule = null): Response
+    public function actionEdit(?string $storeHandle = null, ?int $id = null, ?CatalogPricingRule $catalogPricingRule = null): Response
     {
         if ($id === null) {
             $this->requirePermission('commerce-createCatalogPricingRules');
diff --git a/src/controllers/DiscountsController.php b/src/controllers/DiscountsController.php
index af15fcc82c..aa6963f910 100644
--- a/src/controllers/DiscountsController.php
+++ b/src/controllers/DiscountsController.php
@@ -65,7 +65,7 @@ public function init(): void
     /**
      * @throws HttpException
      */
-    public function actionIndex(string $storeHandle = null): Response
+    public function actionIndex(?string $storeHandle = null): Response
     {
         if ($storeHandle) {
             $store = Plugin::getInstance()->getStores()->getStoreByHandle($storeHandle);
@@ -178,7 +178,7 @@ public function actionTableData(): Response
      * @param Discount|null $discount
      * @throws HttpException
      */
-    public function actionEdit(int $id = null, Discount $discount = null, string $storeHandle = null): Response
+    public function actionEdit(?int $id = null, ?Discount $discount = null, ?string $storeHandle = null): Response
     {
         if ($id === null) {
             $this->requirePermission('commerce-createDiscounts');
diff --git a/src/controllers/EmailsController.php b/src/controllers/EmailsController.php
index 2632b4523d..6a2a2d27b3 100644
--- a/src/controllers/EmailsController.php
+++ b/src/controllers/EmailsController.php
@@ -59,7 +59,7 @@ public function actionIndex(): Response
      * @param Email|null $email
      * @throws HttpException
      */
-    public function actionEdit(?string $storeHandle = null, int $id = null, Email $email = null): Response
+    public function actionEdit(?string $storeHandle = null, ?int $id = null, ?Email $email = null): Response
     {
         if ($storeHandle === null || !$store = Plugin::getInstance()->getStores()->getStoreByHandle($storeHandle)) {
             $store = Plugin::getInstance()->getStores()->getPrimaryStore();
diff --git a/src/controllers/GatewaysController.php b/src/controllers/GatewaysController.php
index dfc34b1458..1e4f8e5a58 100644
--- a/src/controllers/GatewaysController.php
+++ b/src/controllers/GatewaysController.php
@@ -75,7 +75,7 @@ public function actionIndex(): Response
      * @throws DeprecationException
      * @throws InvalidConfigException
      */
-    public function actionEdit(?string $storeHandle = null, int $id = null, ?GatewayInterface $gateway = null): Response
+    public function actionEdit(?string $storeHandle = null, ?int $id = null, ?GatewayInterface $gateway = null): Response
     {
         /** @var Gateway|null $gateway */
         $variables = compact('id', 'gateway');
diff --git a/src/controllers/LineItemStatusesController.php b/src/controllers/LineItemStatusesController.php
index 587ae407e9..86406a9459 100644
--- a/src/controllers/LineItemStatusesController.php
+++ b/src/controllers/LineItemStatusesController.php
@@ -55,7 +55,7 @@ public function actionIndex(): Response
      * @param LineItemStatus|null $lineItemStatus
      * @throws HttpException
      */
-    public function actionEdit(?string $storeHandle = null, int $id = null, LineItemStatus $lineItemStatus = null): Response
+    public function actionEdit(?string $storeHandle = null, ?int $id = null, ?LineItemStatus $lineItemStatus = null): Response
     {
         if ($storeHandle === null || !$store = Plugin::getInstance()->getStores()->getStoreByHandle($storeHandle)) {
             $store = Plugin::getInstance()->getStores()->getPrimaryStore();
diff --git a/src/controllers/OrderStatusesController.php b/src/controllers/OrderStatusesController.php
index 76b061f11c..ed425a73e8 100644
--- a/src/controllers/OrderStatusesController.php
+++ b/src/controllers/OrderStatusesController.php
@@ -55,7 +55,7 @@ public function actionIndex(): Response
      * @param OrderStatus|null $orderStatus
      * @throws HttpException
      */
-    public function actionEdit(?string $storeHandle = null, int $id = null, OrderStatus $orderStatus = null): Response
+    public function actionEdit(?string $storeHandle = null, ?int $id = null, ?OrderStatus $orderStatus = null): Response
     {
         $variables = compact('id', 'orderStatus');
         if ($storeHandle === null || !$store = Plugin::getInstance()->getStores()->getStoreByHandle($storeHandle)) {
diff --git a/src/controllers/OrdersController.php b/src/controllers/OrdersController.php
index 6ea8e66767..6a80c0aa3c 100644
--- a/src/controllers/OrdersController.php
+++ b/src/controllers/OrdersController.php
@@ -129,7 +129,7 @@ public function init(): void
      *
      * @throws Throwable
      */
-    public function actionOrderIndex(string $orderStatusHandle = ''): Response
+    public function actionOrderIndex(?string $orderStatusHandle = ''): Response
     {
         Craft::$app->getView()->registerAssetBundle(CommerceCpAsset::class);
 
@@ -213,7 +213,7 @@ public function actionCreate(string $storeHandle): Response
      * @throws RuntimeError
      * @throws SyntaxError
      */
-    public function actionEditOrder(int $orderId, Order $order = null, $paymentForm = null): Response
+    public function actionEditOrder(int $orderId, ?Order $order = null, $paymentForm = null): Response
     {
         $plugin = Plugin::getInstance();
         $variables = [];
diff --git a/src/controllers/PaymentCurrenciesController.php b/src/controllers/PaymentCurrenciesController.php
index a3a4e89a22..3f287f6ed4 100644
--- a/src/controllers/PaymentCurrenciesController.php
+++ b/src/controllers/PaymentCurrenciesController.php
@@ -47,7 +47,7 @@ public function actionIndex(?string $storeHandle = null): Response
      * @throws HttpException
      * @throws InvalidConfigException
      */
-    public function actionEdit(int $id = null, PaymentCurrency $currency = null, string $storeHandle = null): Response
+    public function actionEdit(?int $id = null, ?PaymentCurrency $currency = null, ?string $storeHandle = null): Response
     {
         $variables = compact('id', 'currency');
 
diff --git a/src/controllers/PdfsController.php b/src/controllers/PdfsController.php
index 5f8e6c772c..d05ac8216a 100644
--- a/src/controllers/PdfsController.php
+++ b/src/controllers/PdfsController.php
@@ -62,7 +62,7 @@ public function actionIndex(): Response
      * @throws InvalidConfigException
      * @since 3.2
      */
-    public function actionEdit(?string $storeHandle = null, int $id = null, Pdf $pdf = null): Response
+    public function actionEdit(?string $storeHandle = null, ?int $id = null, ?Pdf $pdf = null): Response
     {
         if ($storeHandle === null || !$store = Plugin::getInstance()->getStores()->getStoreByHandle($storeHandle)) {
             $store = Plugin::getInstance()->getStores()->getPrimaryStore();
diff --git a/src/controllers/PlansController.php b/src/controllers/PlansController.php
index dbe65cb45b..6bbc723f12 100644
--- a/src/controllers/PlansController.php
+++ b/src/controllers/PlansController.php
@@ -66,7 +66,7 @@ public function actionPlanIndex(): Response
      * @throws DeprecationException
      * @throws ForbiddenHttpException
      */
-    public function actionEditPlan(int $planId = null, Plan $plan = null): Response
+    public function actionEditPlan(?int $planId = null, ?Plan $plan = null): Response
     {
         $this->requirePermission('commerce-manageSubscriptions');
 
diff --git a/src/controllers/ProductTypesController.php b/src/controllers/ProductTypesController.php
index 718f2b6266..3bd979f722 100644
--- a/src/controllers/ProductTypesController.php
+++ b/src/controllers/ProductTypesController.php
@@ -44,7 +44,7 @@ public function actionProductTypeIndex(): Response
      * @param ProductType|null $productType
      * @throws HttpException
      */
-    public function actionEditProductType(int $productTypeId = null, ProductType $productType = null): Response
+    public function actionEditProductType(?int $productTypeId = null, ?ProductType $productType = null): Response
     {
         $variables = compact('productTypeId', 'productType');
 
diff --git a/src/controllers/SalesController.php b/src/controllers/SalesController.php
index 49df5538f2..67c98746cd 100644
--- a/src/controllers/SalesController.php
+++ b/src/controllers/SalesController.php
@@ -74,7 +74,7 @@ public function actionIndex(?string $storeHandle = null): Response
      * @throws HttpException
      * @throws InvalidConfigException
      */
-    public function actionEdit(int $id = null, Sale $sale = null, ?string $storeHandle = null): Response
+    public function actionEdit(?int $id = null, ?Sale $sale = null, ?string $storeHandle = null): Response
     {
         if ($id === null) {
             $this->requirePermission('commerce-createSales');
diff --git a/src/controllers/ShippingCategoriesController.php b/src/controllers/ShippingCategoriesController.php
index 0d27d8d158..9eb0eba789 100644
--- a/src/controllers/ShippingCategoriesController.php
+++ b/src/controllers/ShippingCategoriesController.php
@@ -51,7 +51,7 @@ public function actionIndex(?string $storeHandle = null): Response
      * @param ShippingCategory|null $shippingCategory
      * @throws HttpException
      */
-    public function actionEdit(?string $storeHandle = null, int $id = null, ShippingCategory $shippingCategory = null): Response
+    public function actionEdit(?string $storeHandle = null, ?int $id = null, ?ShippingCategory $shippingCategory = null): Response
     {
         $variables = [
             'id' => $id,
diff --git a/src/controllers/ShippingMethodsController.php b/src/controllers/ShippingMethodsController.php
index 9b2ada9723..0aea09801f 100644
--- a/src/controllers/ShippingMethodsController.php
+++ b/src/controllers/ShippingMethodsController.php
@@ -45,7 +45,7 @@ public function actionIndex(?string $storeHandle = null): Response
      * @throws HttpException
      * @throws InvalidConfigException
      */
-    public function actionEdit(?string $storeHandle = null, int $id = null, ShippingMethod $shippingMethod = null): Response
+    public function actionEdit(?string $storeHandle = null, ?int $id = null, ?ShippingMethod $shippingMethod = null): Response
     {
         if ($storeHandle === null || !$store = Plugin::getInstance()->getStores()->getStoreByHandle($storeHandle)) {
             $store = Plugin::getInstance()->getStores()->getPrimaryStore();
diff --git a/src/controllers/ShippingRulesController.php b/src/controllers/ShippingRulesController.php
index 5f3aadfc13..d694d413e1 100644
--- a/src/controllers/ShippingRulesController.php
+++ b/src/controllers/ShippingRulesController.php
@@ -48,7 +48,7 @@ class ShippingRulesController extends BaseShippingSettingsController
      * @throws SyntaxError
      * @throws Exception
      */
-    public function actionEdit(?string $storeHandle = null, int $methodId = null, int $ruleId = null, ShippingRule $shippingRule = null): Response
+    public function actionEdit(?string $storeHandle = null, ?int $methodId = null, ?int $ruleId = null, ?ShippingRule $shippingRule = null): Response
     {
         if ($storeHandle === null || !$store = Plugin::getInstance()->getStores()->getStoreByHandle($storeHandle)) {
             $store = Plugin::getInstance()->getStores()->getPrimaryStore();
diff --git a/src/controllers/ShippingZonesController.php b/src/controllers/ShippingZonesController.php
index 9d3a6627d4..36ccea56eb 100644
--- a/src/controllers/ShippingZonesController.php
+++ b/src/controllers/ShippingZonesController.php
@@ -42,7 +42,7 @@ public function actionIndex(?string $storeHandle = null): Response
      * @param ShippingAddressZone|null $shippingZone
      * @throws HttpException
      */
-    public function actionEdit(?string $storeHandle = null, int $id = null, ShippingAddressZone $shippingZone = null): Response
+    public function actionEdit(?string $storeHandle = null, ?int $id = null, ?ShippingAddressZone $shippingZone = null): Response
     {
         if ($storeHandle === null || !$store = Plugin::getInstance()->getStores()->getStoreByHandle($storeHandle)) {
             $store = Plugin::getInstance()->getStores()->getPrimaryStore();
diff --git a/src/controllers/StoreManagementController.php b/src/controllers/StoreManagementController.php
index 9e9d2ee56e..98bf0fbfb8 100644
--- a/src/controllers/StoreManagementController.php
+++ b/src/controllers/StoreManagementController.php
@@ -67,7 +67,7 @@ public function actionIndex(): Response
      * @throws TemplateLoaderException
      * @throws InvalidConfigException
      */
-    public function actionEdit(StoreSettings $storeSettings = null, ?string $storeHandle = null): Response
+    public function actionEdit(?StoreSettings $storeSettings = null, ?string $storeHandle = null): Response
     {
         $this->requirePermission('commerce-manageGeneralStoreSettings');
 
diff --git a/src/controllers/StoresController.php b/src/controllers/StoresController.php
index 6c48478a01..d0efbe235d 100644
--- a/src/controllers/StoresController.php
+++ b/src/controllers/StoresController.php
@@ -332,7 +332,7 @@ public function actionReorderStores(): Response
      * @return Response
      * @throws InvalidConfigException
      */
-    public function actionEditSiteStores(Collection $sitesStores = null): Response
+    public function actionEditSiteStores(?Collection $sitesStores = null): Response
     {
         // Breadcrumbs
         $crumbs = [
diff --git a/src/controllers/SubscriptionsController.php b/src/controllers/SubscriptionsController.php
index 3c54a21303..1f4174a623 100644
--- a/src/controllers/SubscriptionsController.php
+++ b/src/controllers/SubscriptionsController.php
@@ -53,7 +53,7 @@ public function actionIndex(): Response
      * @throws HttpException
      * @throws InvalidConfigException
      */
-    public function actionEdit(int $subscriptionId = null, Subscription $subscription = null): Response
+    public function actionEdit(?int $subscriptionId = null, ?Subscription $subscription = null): Response
     {
         $variables = [];
 
diff --git a/src/controllers/TaxCategoriesController.php b/src/controllers/TaxCategoriesController.php
index 10297a53a1..61332709a5 100644
--- a/src/controllers/TaxCategoriesController.php
+++ b/src/controllers/TaxCategoriesController.php
@@ -48,7 +48,7 @@ public function actionIndex(?string $storeHandle = null): Response
      * @param TaxCategory|null $taxCategory
      * @throws HttpException
      */
-    public function actionEdit(?string $storeHandle = null, int $id = null, TaxCategory $taxCategory = null): Response
+    public function actionEdit(?string $storeHandle = null, ?int $id = null, ?TaxCategory $taxCategory = null): Response
     {
         if ($storeHandle === null || !$store = Plugin::getInstance()->getStores()->getStoreByHandle($storeHandle)) {
             $store = Plugin::getInstance()->getStores()->getPrimaryStore();
diff --git a/src/controllers/TaxRatesController.php b/src/controllers/TaxRatesController.php
index babaaf34db..cf811f2dc1 100644
--- a/src/controllers/TaxRatesController.php
+++ b/src/controllers/TaxRatesController.php
@@ -71,7 +71,7 @@ public function actionIndex(?string $storeHandle = null): Response
      * @throws SyntaxError
      * @throws Exception
      */
-    public function actionEdit(?string $storeHandle = null, int $id = null, TaxRate $taxRate = null): Response
+    public function actionEdit(?string $storeHandle = null, ?int $id = null, ?TaxRate $taxRate = null): Response
     {
         if (!Plugin::getInstance()->getTaxes()->viewTaxRates()) {
             throw new ForbiddenHttpException('Tax engine does not permit you to perform this action');
diff --git a/src/controllers/TaxZonesController.php b/src/controllers/TaxZonesController.php
index a3e890c745..1fa5978104 100644
--- a/src/controllers/TaxZonesController.php
+++ b/src/controllers/TaxZonesController.php
@@ -50,7 +50,7 @@ public function actionIndex(?string $storeHandle = null): Response
      * @param TaxAddressZone|null $taxZone
      * @throws HttpException
      */
-    public function actionEdit(?string $storeHandle = null, int $id = null, TaxAddressZone $taxZone = null): Response
+    public function actionEdit(?string $storeHandle = null, ?int $id = null, ?TaxAddressZone $taxZone = null): Response
     {
         if ($storeHandle === null || !$store = Plugin::getInstance()->getStores()->getStoreByHandle($storeHandle)) {
             $store = Plugin::getInstance()->getStores()->getPrimaryStore();
diff --git a/src/elements/Order.php b/src/elements/Order.php
index 2a01fcaf55..03c277d511 100644
--- a/src/elements/Order.php
+++ b/src/elements/Order.php
@@ -2422,7 +2422,7 @@ public function getCpEditUrl(): ?string
      * @param string|null $pdfHandle The handle of the PDF to use. If none is passed the default PDF is used.
      * @return string|null The URL to the order’s PDF invoice, or null if the PDF template doesn’t exist
      */
-    public function getPdfUrl(string $option = null, string $pdfHandle = null): ?string
+    public function getPdfUrl(?string $option = null, ?string $pdfHandle = null): ?string
     {
         $path = "commerce/downloads/pdf";
         $params = [];
diff --git a/src/elements/Product.php b/src/elements/Product.php
index 496c5b09d1..c8d2dc46f1 100644
--- a/src/elements/Product.php
+++ b/src/elements/Product.php
@@ -219,7 +219,7 @@ public static function createCondition(): ElementConditionInterface
     /**
      * @inheritdoc
      */
-    protected static function defineSources(string $context = null): array
+    protected static function defineSources(?string $context = null): array
     {
         if ($context == 'index') {
             $productTypes = Plugin::getInstance()->getProductTypes()->getEditableProductTypes();
@@ -334,7 +334,7 @@ protected static function defineFieldLayouts(?string $source): array
     /**
      * @inheritdoc
      */
-    protected static function defineActions(string $source = null): array
+    protected static function defineActions(?string $source = null): array
     {
         $elementsService = Craft::$app->getElements();
         // Get the selected site
@@ -1107,7 +1107,15 @@ public function getVariants(bool $includeDisabled = false): VariantCollection
                 return VariantCollection::make();
             }
 
-            $variants = self::createVariantQuery($this)->status(null)->collect();
+            /** @var self|null $duplicatingProduct */
+            $duplicatingProduct = $this->duplicateOf;
+            if ($duplicatingProduct) {
+                $query = self::createVariantQuery($duplicatingProduct)->status(null);
+            } else {
+                $query = self::createVariantQuery($this)->status(null);
+            }
+
+            $variants = $query->collect();
 
             // Don't memoize empty collections in favour of a new query next time
             if ($variants->isEmpty()) {
@@ -1885,12 +1893,9 @@ protected static function defineSearchableAttributes(): array
      */
     private static function createVariantQuery(Product $product): VariantQuery
     {
-        $productId = $product->duplicateOf?->id ?? $product->id;
-        $productSiteId = $product->duplicateOf?->siteId ?? $product->siteId;
-
         $query = Variant::find()
-            ->productId($productId)
-            ->siteId($productSiteId)
+            ->productId($product->id)
+            ->siteId($product->siteId)
             ->orderBy(['sortOrder' => SORT_ASC]);
 
         if ($product->getIsRevision()) {
diff --git a/src/elements/Subscription.php b/src/elements/Subscription.php
index 71cb718aaa..9d09a49c4b 100644
--- a/src/elements/Subscription.php
+++ b/src/elements/Subscription.php
@@ -435,7 +435,7 @@ public function getStatus(): ?string
     /**
      * @inheritdoc
      */
-    public static function defineSources(string $context = null): array
+    public static function defineSources(?string $context = null): array
     {
         $plans = Plugin::getInstance()->getPlans()->getAllPlans();
 
diff --git a/src/elements/Transfer.php b/src/elements/Transfer.php
index a56ff033d8..ce7c830b21 100644
--- a/src/elements/Transfer.php
+++ b/src/elements/Transfer.php
@@ -443,7 +443,7 @@ public function getUriFormat(): ?string
      * @param string|null $context
      * @return array
      */
-    protected static function defineSources(string $context = null): array
+    protected static function defineSources(?string $context = null): array
     {
         $transferStatuses = TransferStatusType::cases();
         $transferStatusSources = [];
diff --git a/src/elements/Variant.php b/src/elements/Variant.php
index dd6d1b2e4b..9ff4ce5a64 100755
--- a/src/elements/Variant.php
+++ b/src/elements/Variant.php
@@ -881,30 +881,34 @@ public static function hasStatuses(): bool
      */
     public static function eagerLoadingMap(array $sourceElements, string $handle): array|null|false
     {
-        if (in_array($handle, ['product', 'owner', 'primaryOwner'])) {
-            // Get the source element IDs
-            $sourceElementIds = [];
+        switch ($handle) {
+            case 'product':
+                // Get the source element IDs
+                $sourceElementIds = [];
 
-            foreach ($sourceElements as $sourceElement) {
-                $sourceElementIds[] = $sourceElement->id;
-            }
+                foreach ($sourceElements as $sourceElement) {
+                    $sourceElementIds[] = $sourceElement->id;
+                }
 
-            $map = (new Query())
-                ->select('id as source, primaryOwnerId as target')
-                ->from(Table::VARIANTS)
-                ->where(['in', 'id', $sourceElementIds])
-                ->all();
-
-            return [
-                'elementType' => Product::class,
-                'map' => $map,
-                'criteria' => [
-                    'status' => null,
-                ],
-            ];
+                $map = (new Query())
+                    ->select('id as source, primaryOwnerId as target')
+                    ->from(Table::VARIANTS)
+                    ->where(['in', 'id', $sourceElementIds])
+                    ->all();
+
+                return [
+                    'elementType' => Product::class,
+                    'map' => $map,
+                    'criteria' => [
+                        'status' => null,
+                    ],
+                ];
+            default:
+                return array_merge(
+                    self::traitEagerLoadingMap($sourceElements, $handle),
+                    ['elementType' => Product::class],
+                );
         }
-
-        return self::traitEagerLoadingMap($sourceElements, $handle);
     }
 
     /**
@@ -1041,18 +1045,24 @@ public function afterSave(bool $isNew): void
                         ->max('[[eo.sortOrder]]');
                     $this->sortOrder = $max ? $max + 1 : 1;
                 }
-                if ($isNew) {
-                    Db::insert(CraftTable::ELEMENTS_OWNERS, [
+
+                $ownerIds = array_unique([
+                    $ownerId,
+                    $this->getPrimaryOwnerId(),
+                ]);
+
+                if (!$isNew) {
+                    Db::delete(CraftTAble::ELEMENTS_OWNERS, [
                         'elementId' => $this->id,
-                        'ownerId' => $ownerId,
-                        'sortOrder' => $this->sortOrder,
+                        'ownerId' => $ownerIds,
                     ]);
-                } else {
-                    Db::update(CraftTable::ELEMENTS_OWNERS, [
-                        'sortOrder' => $this->sortOrder,
-                    ], [
+                }
+
+                foreach ($ownerIds as $ownerId) {
+                    Db::insert(CraftTAble::ELEMENTS_OWNERS, [
                         'elementId' => $this->id,
                         'ownerId' => $ownerId,
+                        'sortOrder' => $this->sortOrder,
                     ]);
                 }
             }
@@ -1292,7 +1302,7 @@ protected function availableTaxCategories(): array
     /**
      * @inheritdoc
      */
-    protected static function defineSources(string $context = null): array
+    protected static function defineSources(?string $context = null): array
     {
         $sources = Product::defineSources($context);
 
diff --git a/src/elements/traits/OrderElementTrait.php b/src/elements/traits/OrderElementTrait.php
index 5a8e74a584..b380f4c8b4 100644
--- a/src/elements/traits/OrderElementTrait.php
+++ b/src/elements/traits/OrderElementTrait.php
@@ -294,7 +294,7 @@ public function getSearchKeywords(string $attribute): string
      * @inheritdoc
      * @throws Exception
      */
-    protected static function defineSources(string $context = null): array
+    protected static function defineSources(?string $context = null): array
     {
         $siteHandle = Craft::$app->getRequest()->getParam('site');
         $site = $siteHandle ? Craft::$app->getSites()->getSiteByHandle($siteHandle) : Craft::$app->getSites()->getCurrentSite();
@@ -505,7 +505,7 @@ protected static function defineTableAttributes(): array
     /**
      * @inheritdoc
      */
-    protected static function defineDefaultTableAttributes(string $source = null): array
+    protected static function defineDefaultTableAttributes(?string $source = null): array
     {
         $attributes = [];
         $attributes[] = 'order';
diff --git a/src/fieldlayoutelements/ProductTitleField.php b/src/fieldlayoutelements/ProductTitleField.php
index 372c182cea..5b3b8173cb 100644
--- a/src/fieldlayoutelements/ProductTitleField.php
+++ b/src/fieldlayoutelements/ProductTitleField.php
@@ -62,7 +62,7 @@ protected function translationDescription(?ElementInterface $element = null, boo
     /**
      * @inheritdoc
      */
-    public function inputHtml(ElementInterface $element = null, bool $static = false): ?string
+    public function inputHtml(?ElementInterface $element = null, bool $static = false): ?string
     {
         if (!$element instanceof Product) {
             throw new InvalidArgumentException('ProductTitleField can only be used in product field layouts.');
diff --git a/src/fieldlayoutelements/PurchasableAllowedQtyField.php b/src/fieldlayoutelements/PurchasableAllowedQtyField.php
index 302b2f29cb..af08dcbb4c 100644
--- a/src/fieldlayoutelements/PurchasableAllowedQtyField.php
+++ b/src/fieldlayoutelements/PurchasableAllowedQtyField.php
@@ -45,7 +45,7 @@ public function __construct(array $config = [])
     /**
      * @inheritdoc
      */
-    public function inputHtml(ElementInterface $element = null, bool $static = false): ?string
+    public function inputHtml(?ElementInterface $element = null, bool $static = false): ?string
     {
         if (!$element instanceof Purchasable) {
             throw new InvalidArgumentException(static::class . ' can only be used in purchasable field layouts.');
diff --git a/src/fieldlayoutelements/PurchasableAvailableForPurchaseField.php b/src/fieldlayoutelements/PurchasableAvailableForPurchaseField.php
index 455c920f7c..8969b73105 100644
--- a/src/fieldlayoutelements/PurchasableAvailableForPurchaseField.php
+++ b/src/fieldlayoutelements/PurchasableAvailableForPurchaseField.php
@@ -50,7 +50,7 @@ public function __construct(array $config = [])
     /**
      * @inheritdoc
      */
-    public function inputHtml(ElementInterface $element = null, bool $static = false): ?string
+    public function inputHtml(?ElementInterface $element = null, bool $static = false): ?string
     {
         if (!$element instanceof Purchasable) {
             throw new InvalidArgumentException(static::class . ' can only be used in purchasable field layouts.');
diff --git a/src/fieldlayoutelements/PurchasableDimensionsField.php b/src/fieldlayoutelements/PurchasableDimensionsField.php
index 89c693f4f2..4bb8caeba6 100644
--- a/src/fieldlayoutelements/PurchasableDimensionsField.php
+++ b/src/fieldlayoutelements/PurchasableDimensionsField.php
@@ -58,7 +58,7 @@ public function showInForm(?ElementInterface $element = null): bool
     /**
      * @inheritdoc
      */
-    public function inputHtml(ElementInterface $element = null, bool $static = false): ?string
+    public function inputHtml(?ElementInterface $element = null, bool $static = false): ?string
     {
         if (!$element instanceof Purchasable) {
             throw new InvalidArgumentException(static::class . ' can only be used in purchasable field layouts.');
diff --git a/src/fieldlayoutelements/PurchasableFreeShippingField.php b/src/fieldlayoutelements/PurchasableFreeShippingField.php
index 3158fcd551..2c44ae4037 100644
--- a/src/fieldlayoutelements/PurchasableFreeShippingField.php
+++ b/src/fieldlayoutelements/PurchasableFreeShippingField.php
@@ -44,7 +44,7 @@ public function __construct(array $config = [])
     /**
      * @inheritdoc
      */
-    public function inputHtml(ElementInterface $element = null, bool $static = false): ?string
+    public function inputHtml(?ElementInterface $element = null, bool $static = false): ?string
     {
         if (!$element instanceof Purchasable) {
             throw new InvalidArgumentException(static::class . ' can only be used in purchasable field layouts.');
diff --git a/src/fieldlayoutelements/PurchasablePriceField.php b/src/fieldlayoutelements/PurchasablePriceField.php
index fde9f48c78..a8042dc65f 100755
--- a/src/fieldlayoutelements/PurchasablePriceField.php
+++ b/src/fieldlayoutelements/PurchasablePriceField.php
@@ -63,7 +63,7 @@ protected function defaultLabel(?ElementInterface $element = null, bool $static
     /**
      * @inheritdoc
      */
-    public function inputHtml(ElementInterface $element = null, bool $static = false): ?string
+    public function inputHtml(?ElementInterface $element = null, bool $static = false): ?string
     {
         $view = Craft::$app->getView();
         $view->registerAssetBundle(HtmxAsset::class);
diff --git a/src/fieldlayoutelements/PurchasablePromotableField.php b/src/fieldlayoutelements/PurchasablePromotableField.php
index f3789bb2f8..793cebdb21 100644
--- a/src/fieldlayoutelements/PurchasablePromotableField.php
+++ b/src/fieldlayoutelements/PurchasablePromotableField.php
@@ -49,7 +49,7 @@ public function __construct(array $config = [])
     /**
      * @inheritdoc
      */
-    public function inputHtml(ElementInterface $element = null, bool $static = false): ?string
+    public function inputHtml(?ElementInterface $element = null, bool $static = false): ?string
     {
         if (!$element instanceof Purchasable) {
             throw new InvalidArgumentException(static::class . ' can only be used in purchasable field layouts.');
diff --git a/src/fieldlayoutelements/PurchasableSkuField.php b/src/fieldlayoutelements/PurchasableSkuField.php
index 3e44319074..12859561df 100644
--- a/src/fieldlayoutelements/PurchasableSkuField.php
+++ b/src/fieldlayoutelements/PurchasableSkuField.php
@@ -42,7 +42,7 @@ class PurchasableSkuField extends BaseNativeField
     /**
      * @inheritdoc
      */
-    public function inputHtml(ElementInterface $element = null, bool $static = false): ?string
+    public function inputHtml(?ElementInterface $element = null, bool $static = false): ?string
     {
         if (!$element instanceof Purchasable) {
             throw new InvalidArgumentException(static::class . ' can only be used in purchasable field layouts.');
diff --git a/src/fieldlayoutelements/PurchasableStockField.php b/src/fieldlayoutelements/PurchasableStockField.php
index 0fd969e8c7..3be80edf59 100644
--- a/src/fieldlayoutelements/PurchasableStockField.php
+++ b/src/fieldlayoutelements/PurchasableStockField.php
@@ -59,7 +59,7 @@ public function __construct(array $config = [])
     /**
      * @inheritdoc
      */
-    public function inputHtml(ElementInterface $element = null, bool $static = false): ?string
+    public function inputHtml(?ElementInterface $element = null, bool $static = false): ?string
     {
         // If this is a revision get the canonical element to show the stock for.
         // @TODO re-evaluate this when we have a better way to handle revisions and inventory.
diff --git a/src/fieldlayoutelements/PurchasableWeightField.php b/src/fieldlayoutelements/PurchasableWeightField.php
index 92429e9698..28ab951929 100755
--- a/src/fieldlayoutelements/PurchasableWeightField.php
+++ b/src/fieldlayoutelements/PurchasableWeightField.php
@@ -57,7 +57,7 @@ public function showInForm(?ElementInterface $element = null): bool
     /**
      * @inheritdoc
      */
-    public function inputHtml(ElementInterface $element = null, bool $static = false): ?string
+    public function inputHtml(?ElementInterface $element = null, bool $static = false): ?string
     {
         if (!$element instanceof Purchasable) {
             throw new InvalidArgumentException(static::class . ' can only be used in purchasable field layouts.');
diff --git a/src/fieldlayoutelements/TransferManagementField.php b/src/fieldlayoutelements/TransferManagementField.php
index 37866dce1a..89abd927e4 100644
--- a/src/fieldlayoutelements/TransferManagementField.php
+++ b/src/fieldlayoutelements/TransferManagementField.php
@@ -50,7 +50,7 @@ class TransferManagementField extends BaseNativeField
     /**
      * @inheritdoc
      */
-    public function inputHtml(ElementInterface $element = null, bool $static = false): ?string
+    public function inputHtml(?ElementInterface $element = null, bool $static = false): ?string
     {
         if (!$element instanceof Transfer) {
             throw new InvalidArgumentException('TransferLocationsField can only be used in transfer field layouts.');
diff --git a/src/fieldlayoutelements/UserAddressSettings.php b/src/fieldlayoutelements/UserAddressSettings.php
index c234d43e59..885c48fd0a 100644
--- a/src/fieldlayoutelements/UserAddressSettings.php
+++ b/src/fieldlayoutelements/UserAddressSettings.php
@@ -56,7 +56,7 @@ protected function useFieldset(): bool
     /**
      * @inheritdoc
      */
-    protected function defaultLabel(ElementInterface $element = null, bool $static = false): ?string
+    protected function defaultLabel(?ElementInterface $element = null, bool $static = false): ?string
     {
         return Craft::t('commerce', 'Commerce Settings');
     }
diff --git a/src/fieldlayoutelements/VariantTitleField.php b/src/fieldlayoutelements/VariantTitleField.php
index 2ca44fa4ab..c5569fd522 100644
--- a/src/fieldlayoutelements/VariantTitleField.php
+++ b/src/fieldlayoutelements/VariantTitleField.php
@@ -62,7 +62,7 @@ protected function translationDescription(?ElementInterface $element = null, boo
     /**
      * @inheritdoc
      */
-    public function inputHtml(ElementInterface $element = null, bool $static = false): ?string
+    public function inputHtml(?ElementInterface $element = null, bool $static = false): ?string
     {
         if (!$element instanceof Variant) {
             throw new InvalidArgumentException('VariantTitleField can only be used in variant field layouts.');
diff --git a/src/fieldlayoutelements/VariantsField.php b/src/fieldlayoutelements/VariantsField.php
index ceef5f02d6..bba397b2f2 100644
--- a/src/fieldlayoutelements/VariantsField.php
+++ b/src/fieldlayoutelements/VariantsField.php
@@ -43,7 +43,7 @@ public function hasCustomWidth(): bool
     /**
      * @inheritdoc
      */
-    protected function defaultLabel(ElementInterface $element = null, bool $static = false): ?string
+    protected function defaultLabel(?ElementInterface $element = null, bool $static = false): ?string
     {
         return Craft::t('commerce', 'Variants');
     }
@@ -51,7 +51,7 @@ protected function defaultLabel(ElementInterface $element = null, bool $static =
     /**
      * @inheritdoc
      */
-    protected function inputHtml(ElementInterface $element = null, bool $static = false): ?string
+    protected function inputHtml(?ElementInterface $element = null, bool $static = false): ?string
     {
         if (!$element instanceof Product) {
             throw new InvalidArgumentException('ProductTitleField can only be used in product field layouts.');
diff --git a/src/models/Email.php b/src/models/Email.php
index 7fa88f5fd4..8062f364fd 100644
--- a/src/models/Email.php
+++ b/src/models/Email.php
@@ -148,7 +148,7 @@ public function extraFields(): array
      *
      * @param Order|null $order
      */
-    public function getRenderLanguage(Order $order = null): string
+    public function getRenderLanguage(?Order $order = null): string
     {
         $language = $this->language;
 
diff --git a/src/models/LineItem.php b/src/models/LineItem.php
index 548dd7cd0f..9b36a97138 100755
--- a/src/models/LineItem.php
+++ b/src/models/LineItem.php
@@ -317,7 +317,7 @@ public function getLineItemStatus(): ?LineItemStatus
      * @param LineItemStatus|null $status
      * @since 3.2.2
      */
-    public function setLineItemStatus(LineItemStatus $status = null): void
+    public function setLineItemStatus(?LineItemStatus $status = null): void
     {
         if ($status !== null) {
             $this->_lineItemStatus = $status;
diff --git a/src/models/Pdf.php b/src/models/Pdf.php
index 7e4d070188..deda0ef6ef 100644
--- a/src/models/Pdf.php
+++ b/src/models/Pdf.php
@@ -165,7 +165,7 @@ public function extraFields(): array
      *
      * @param Order|null $order
      */
-    public function getRenderLanguage(Order $order = null): string
+    public function getRenderLanguage(?Order $order = null): string
     {
         $language = $this->language;
 
diff --git a/src/models/Settings.php b/src/models/Settings.php
index 5dde3db3a1..4042d14b19 100644
--- a/src/models/Settings.php
+++ b/src/models/Settings.php
@@ -297,7 +297,7 @@ public function getDimensionUnits(): array
      * @throws InvalidConfigException if the currency in the config file is not set up
      * @throws SiteNotFoundException
      */
-    public function getPaymentCurrency(string $siteHandle = null): ?string
+    public function getPaymentCurrency(?string $siteHandle = null): ?string
     {
         /** @var Site|StoreBehavior|null $site */
         $site = $siteHandle ? Craft::$app->getSites()->getSiteByHandle($siteHandle) : Craft::$app->getSites()->getPrimarySite();
diff --git a/src/services/CatalogPricing.php b/src/services/CatalogPricing.php
index 1c66ebd974..8ea2370c40 100755
--- a/src/services/CatalogPricing.php
+++ b/src/services/CatalogPricing.php
@@ -67,7 +67,7 @@ private function setQueueProgress(Queue|QueueInterface|null $queue, float $progr
      * @throws Exception
      * @throws InvalidConfigException
      */
-    public function generateCatalogPrices(?array $purchasableIds = null, ?array $catalogPricingRules = null, bool $showConsoleOutput = false, Queue|QueueInterface $queue = null): void
+    public function generateCatalogPrices(?array $purchasableIds = null, ?array $catalogPricingRules = null, bool $showConsoleOutput = false, Queue|QueueInterface|null $queue = null): void
     {
         $chunkSize = 1000;
         $this->setQueueProgress($queue, 10, 'Retrieving purchasables');
diff --git a/src/services/Discounts.php b/src/services/Discounts.php
index bace3f3368..10de476888 100644
--- a/src/services/Discounts.php
+++ b/src/services/Discounts.php
@@ -448,7 +448,7 @@ public function getAllActiveDiscounts(?Order $order = null): array
      * @throws InvalidConfigException
      * @throws \Exception
      */
-    public function orderCouponAvailable(Order $order, string &$explanation = null): bool
+    public function orderCouponAvailable(Order $order, ?string &$explanation = null): bool
     {
         $discount = $this->getDiscountByCode($order->couponCode, $order->storeId);
 
diff --git a/src/services/LineItems.php b/src/services/LineItems.php
index 52e945b769..ef92d7301c 100644
--- a/src/services/LineItems.php
+++ b/src/services/LineItems.php
@@ -391,7 +391,7 @@ public function getLineItemById(int $id): ?LineItem
      * @throws \Exception
      * @deprecated in 5.1.0. Use [[create()]] instead.
      */
-    public function createLineItem(Order $order, int $purchasableId, array $options, int $qty = 1, string $note = '', string $uid = null): LineItem
+    public function createLineItem(Order $order, int $purchasableId, array $options, int $qty = 1, string $note = '', ?string $uid = null): LineItem
     {
         Craft::$app->getDeprecator()->log(__METHOD__, 'LineItems::createLineItem() has been deprecated. Use LineItems::create() instead.');
         $lineItem = new LineItem();
diff --git a/src/services/PaymentSources.php b/src/services/PaymentSources.php
index 8542df7adb..f61567526b 100644
--- a/src/services/PaymentSources.php
+++ b/src/services/PaymentSources.php
@@ -147,7 +147,7 @@ public function getAllPaymentSourcesByCustomerId(?int $customerId = null, ?int $
      * @return Collection
      * @throws InvalidConfigException
      */
-    public function getAllPaymentSourcesByGatewayId(int $gatewayId = null): Collection
+    public function getAllPaymentSourcesByGatewayId(?int $gatewayId = null): Collection
     {
         if ($gatewayId === null) {
             return collect();
@@ -177,7 +177,7 @@ public function getAllPaymentSourcesByGatewayId(int $gatewayId = null): Collecti
      * @return Collection<PaymentSource>
      * @throws InvalidConfigException
      */
-    public function getAllGatewayPaymentSourcesByCustomerId(int $gatewayId = null, int $customerId = null): Collection
+    public function getAllGatewayPaymentSourcesByCustomerId(?int $gatewayId = null, ?int $customerId = null): Collection
     {
         if ($gatewayId === null || $customerId === null) {
             return collect();
@@ -263,7 +263,7 @@ public function getPaymentSourceByIdAndUserId(int $sourceId, int $userId): ?Paym
      * @throws InvalidConfigException
      * @throws PaymentSourceException If unable to create the payment source
      */
-    public function createPaymentSource(int $customerId, GatewayInterface $gateway, BasePaymentForm $paymentForm, string $sourceDescription = null, bool $makePrimarySource = false): PaymentSource
+    public function createPaymentSource(int $customerId, GatewayInterface $gateway, BasePaymentForm $paymentForm, ?string $sourceDescription = null, bool $makePrimarySource = false): PaymentSource
     {
         $source = $gateway->createPaymentSource($paymentForm, $customerId);
 
diff --git a/src/services/Payments.php b/src/services/Payments.php
index ef88aee4b7..fd8c97041d 100644
--- a/src/services/Payments.php
+++ b/src/services/Payments.php
@@ -566,7 +566,7 @@ private function _capture(Transaction $parent): Transaction
      * @param string $note the administrators note on the refund
      * @throws RefundException if anything goes wrong during a refund
      */
-    private function _refund(Transaction $parent, float $amount = null, string $note = ''): Transaction
+    private function _refund(Transaction $parent, ?float $amount = null, string $note = ''): Transaction
     {
         try {
             $gateway = $parent->getGateway();
diff --git a/src/services/Pdfs.php b/src/services/Pdfs.php
index f2b371ecac..e1f7cb0eb1 100644
--- a/src/services/Pdfs.php
+++ b/src/services/Pdfs.php
@@ -466,7 +466,7 @@ public function reorderPdfs(array $ids): bool
      * @return string The PDF data.
      * @throws Exception
      */
-    public function renderPdfForOrder(Order $order, string $option = '', string $templatePath = null, array $variables = [], Pdf $pdf = null): string
+    public function renderPdfForOrder(Order $order, string $option = '', ?string $templatePath = null, array $variables = [], ?Pdf $pdf = null): string
     {
         if ($pdf instanceof Pdf) {
             $templatePath = $pdf->templatePath;
diff --git a/src/services/Products.php b/src/services/Products.php
index 02d500161f..f89d468ee1 100644
--- a/src/services/Products.php
+++ b/src/services/Products.php
@@ -31,7 +31,7 @@ class Products extends Component
      * @param array|int|string|null $siteId
      * @return Product|null
      */
-    public function getProductById(int $id, array|int|string $siteId = null, array $criteria = []): ?Product
+    public function getProductById(int $id, array|int|string|null $siteId = null, array $criteria = []): ?Product
     {
         if (!$id) {
             return null;
diff --git a/src/services/Purchasables.php b/src/services/Purchasables.php
index e7b9629700..62fb8c1e32 100644
--- a/src/services/Purchasables.php
+++ b/src/services/Purchasables.php
@@ -144,7 +144,7 @@ class Purchasables extends Component
      * @throws Throwable
      * @since 5.3.0
      */
-    public function isPurchasableOutOfStockPurchasingAllowed(Purchasable $purchasable, Order $order = null, User $currentUser = null): bool
+    public function isPurchasableOutOfStockPurchasingAllowed(Purchasable $purchasable, ?Order $order = null, ?User $currentUser = null): bool
     {
         if ($currentUser === null) {
             $currentUser = Craft::$app->getUser()->getIdentity();
@@ -166,7 +166,7 @@ public function isPurchasableOutOfStockPurchasingAllowed(Purchasable $purchasabl
      * @param User|null $currentUser
      * @since 3.3.1
      */
-    public function isPurchasableAvailable(PurchasableInterface $purchasable, Order $order = null, User $currentUser = null): bool
+    public function isPurchasableAvailable(PurchasableInterface $purchasable, ?Order $order = null, ?User $currentUser = null): bool
     {
         if ($currentUser === null) {
             $currentUser = Craft::$app->getUser()->getIdentity();
@@ -187,7 +187,7 @@ public function isPurchasableAvailable(PurchasableInterface $purchasable, Order
      * @param User|null $currentUser
      * @since 3.3.2
      */
-    public function isPurchasableShippable(PurchasableInterface $purchasable, Order $order = null, User $currentUser = null): bool
+    public function isPurchasableShippable(PurchasableInterface $purchasable, ?Order $order = null, ?User $currentUser = null): bool
     {
         if ($currentUser === null) {
             $currentUser = Craft::$app->getUser()->getIdentity();
diff --git a/src/services/Sales.php b/src/services/Sales.php
index 1d16a0da2e..116a691b40 100644
--- a/src/services/Sales.php
+++ b/src/services/Sales.php
@@ -273,7 +273,7 @@ public function getAllSales(): array
      * @return Sale[]
      * @throws InvalidConfigException
      */
-    public function getSalesForPurchasable(PurchasableInterface $purchasable, Order $order = null): array
+    public function getSalesForPurchasable(PurchasableInterface $purchasable, ?Order $order = null): array
     {
         $matchedSales = [];
 
@@ -335,7 +335,7 @@ public function getSalesRelatedToPurchasable(PurchasableInterface $purchasable):
      *
      * @param Order|null $order
      */
-    public function getSalePriceForPurchasable(PurchasableInterface $purchasable, Order $order = null): float
+    public function getSalePriceForPurchasable(PurchasableInterface $purchasable, ?Order $order = null): float
     {
         $sales = $this->getSalesForPurchasable($purchasable, $order);
         $originalPrice = $purchasable->getPrice();
@@ -398,7 +398,7 @@ public function getSalePriceForPurchasable(PurchasableInterface $purchasable, Or
      * @param Order|null $order
      * @throws InvalidConfigException
      */
-    public function matchPurchasableAndSale(PurchasableInterface $purchasable, Sale $sale, Order $order = null): bool
+    public function matchPurchasableAndSale(PurchasableInterface $purchasable, Sale $sale, ?Order $order = null): bool
     {
         /** @var Purchasable $purchasable */
         $purchasableId = $purchasable->id;
diff --git a/src/services/Subscriptions.php b/src/services/Subscriptions.php
index 1953b9bde9..24d7cd200b 100644
--- a/src/services/Subscriptions.php
+++ b/src/services/Subscriptions.php
@@ -422,7 +422,7 @@ public function beforeDeleteUserHandler(ModelEvent $event): void
      * @throws Exception
      * @throws Throwable if cannot expire subscription
      */
-    public function expireSubscription(Subscription $subscription, DateTime $dateTime = null): bool
+    public function expireSubscription(Subscription $subscription, ?DateTime $dateTime = null): bool
     {
         $subscription->isExpired = true;
         $subscription->dateExpired = $dateTime;
diff --git a/src/services/Transactions.php b/src/services/Transactions.php
index 55d5ba4b51..4d336c6b3e 100644
--- a/src/services/Transactions.php
+++ b/src/services/Transactions.php
@@ -183,7 +183,7 @@ public function refundableAmountForTransaction(Transaction $transaction): float
      * @throws CurrencyException
      * @throws InvalidConfigException
      */
-    public function createTransaction(Order $order = null, Transaction $parentTransaction = null, ?string $typeOverride = null): Transaction
+    public function createTransaction(?Order $order = null, ?Transaction $parentTransaction = null, ?string $typeOverride = null): Transaction
     {
         if (!$order && !$parentTransaction) {
             throw new TransactionException('Tried to create a transaction without order or parent transaction');
diff --git a/src/services/Variants.php b/src/services/Variants.php
index 3136478288..69fd5eb70a 100644
--- a/src/services/Variants.php
+++ b/src/services/Variants.php
@@ -38,7 +38,7 @@ class Variants extends Component
      * @param int|null $siteId Site ID for which to return the variants. Defaults to `null` which is current site.
      * @return Variant[]
      */
-    public function getAllVariantsByProductId(int $productId, int $siteId = null, bool $includeDisabled = true): array
+    public function getAllVariantsByProductId(int $productId, ?int $siteId = null, bool $includeDisabled = true): array
     {
         $variantQuery = Variant::find()
             ->productId($productId)
@@ -58,7 +58,7 @@ public function getAllVariantsByProductId(int $productId, int $siteId = null, bo
      * @param int $variantId The variant’s ID.
      * @param int|null $siteId The site ID for which to fetch the variant. Defaults to `null` which is current site.
      */
-    public function getVariantById(int $variantId, int $siteId = null): ?Variant
+    public function getVariantById(int $variantId, ?int $siteId = null): ?Variant
     {
         return Craft::$app->getElements()->getElementById($variantId, Variant::class, $siteId);
     }
diff --git a/src/stats/TopCustomers.php b/src/stats/TopCustomers.php
index a2c472e7c7..c7f8d74be6 100644
--- a/src/stats/TopCustomers.php
+++ b/src/stats/TopCustomers.php
@@ -38,7 +38,7 @@ class TopCustomers extends Stat
     /**
      * @inheritDoc
      */
-    public function __construct(string $dateRange = null, string $type = null, $startDate = null, $endDate = null, ?int $storeId = null)
+    public function __construct(?string $dateRange = null, ?string $type = null, $startDate = null, $endDate = null, ?int $storeId = null)
     {
         if ($type) {
             $this->type = $type;
diff --git a/src/stats/TopProductTypes.php b/src/stats/TopProductTypes.php
index a5048c26f0..ae51d04723 100644
--- a/src/stats/TopProductTypes.php
+++ b/src/stats/TopProductTypes.php
@@ -40,7 +40,7 @@ class TopProductTypes extends Stat
     /**
      * @inheritDoc
      */
-    public function __construct(string $dateRange = null, string $type = null, $startDate = null, $endDate = null, ?int $storeId = null)
+    public function __construct(?string $dateRange = null, ?string $type = null, $startDate = null, $endDate = null, ?int $storeId = null)
     {
         $this->type = $type ?? $this->type;
 
diff --git a/src/stats/TopProducts.php b/src/stats/TopProducts.php
index 08975ba76b..861e621689 100644
--- a/src/stats/TopProducts.php
+++ b/src/stats/TopProducts.php
@@ -103,7 +103,7 @@ class TopProducts extends Stat
     /**
      * @inheritDoc
      */
-    public function __construct(string $dateRange = null, string $type = null, $startDate = null, $endDate = null, array $revenueOptions = null, ?int $storeId = null)
+    public function __construct(?string $dateRange = null, ?string $type = null, $startDate = null, $endDate = null, ?array $revenueOptions = null, ?int $storeId = null)
     {
         $this->_ifNullDbFunc = Craft::$app->getDb()->getIsPgsql() ? 'COALESCE' : 'IFNULL';
 
diff --git a/src/stats/TopPurchasables.php b/src/stats/TopPurchasables.php
index ceb6f402ad..6c8a18a1a9 100644
--- a/src/stats/TopPurchasables.php
+++ b/src/stats/TopPurchasables.php
@@ -38,7 +38,7 @@ class TopPurchasables extends Stat
     /**
      * @inheritDoc
      */
-    public function __construct(string $dateRange = null, string $type = null, $startDate = null, $endDate = null, ?int $storeId = null)
+    public function __construct(?string $dateRange = null, ?string $type = null, $startDate = null, $endDate = null, ?int $storeId = null)
     {
         $this->type = $type ?? $this->type;
 
diff --git a/src/stats/TotalOrdersByCountry.php b/src/stats/TotalOrdersByCountry.php
index 4b193a895c..493ca09a3e 100644
--- a/src/stats/TotalOrdersByCountry.php
+++ b/src/stats/TotalOrdersByCountry.php
@@ -36,7 +36,7 @@ class TotalOrdersByCountry extends Stat
     /**
      * @inheritDoc
      */
-    public function __construct(string $dateRange = null, string $type = null, $startDate = null, $endDate = null, ?int $storeId = null)
+    public function __construct(?string $dateRange = null, ?string $type = null, $startDate = null, $endDate = null, ?int $storeId = null)
     {
         $this->type = $type ?? $this->type;
 
diff --git a/tests/unit/elements/product/ProductGetVariantsTest.php b/tests/unit/elements/product/ProductGetVariantsTest.php
index 7fefab35a5..2be28e7ccf 100644
--- a/tests/unit/elements/product/ProductGetVariantsTest.php
+++ b/tests/unit/elements/product/ProductGetVariantsTest.php
@@ -27,7 +27,7 @@ class ProductGetVariantsTest extends Unit
      * @var \UnitTester
      */
     protected $tester;
-    
+
     /**
      * @return array
      */
@@ -47,7 +47,7 @@ public function testGetVariantsReturnsEmptyCollectionForNewProduct(): void
     {
         $product = new Product();
         $variants = $product->getVariants();
-        
+
         self::assertInstanceOf(VariantCollection::class, $variants);
         self::assertTrue($variants->isEmpty());
     }
@@ -60,23 +60,23 @@ public function testGetVariantsDoesNotMemoizeEmptyCollections(): void
         $product = new Product();
         $product->id = 999999; // Non-existent ID
         $product->typeId = 2000;
-        
+
         // First call should return empty collection
         $variants1 = $product->getVariants();
         self::assertTrue($variants1->isEmpty());
-        
+
         // Access private _variants property to check if it was memoized
         $reflection = new ReflectionClass($product);
         $variantsProperty = $reflection->getProperty('_variants');
         $variantsProperty->setAccessible(true);
-        
+
         // Should be null, not an empty collection
         self::assertNull($variantsProperty->getValue($product));
-        
+
         // Second call should also return empty collection (new query)
         $variants2 = $product->getVariants();
         self::assertTrue($variants2->isEmpty());
-        
+
         // Still should not be memoized
         self::assertNull($variantsProperty->getValue($product));
     }
@@ -91,21 +91,21 @@ public function testGetVariantsMemoizesNonEmptyCollections(): void
         $productFixture = $this->tester->grabFixture('products');
         $product = $productFixture->getElement('rad-hoodie');
         self::assertNotNull($product);
-        
+
         // First call
         $variants1 = $product->getVariants();
         self::assertFalse($variants1->isEmpty());
-        
+
         // Access private _variants property
         $reflection = new ReflectionClass($product);
         $variantsProperty = $reflection->getProperty('_variants');
         $variantsProperty->setAccessible(true);
-        
+
         // Should be memoized
         $memoizedVariants = $variantsProperty->getValue($product);
         self::assertInstanceOf(VariantCollection::class, $memoizedVariants);
         self::assertNotNull($memoizedVariants);
-        
+
         // Second call should return the memoized collection
         $variants2 = $product->getVariants();
         self::assertCount($variants1->count(), $variants2);
@@ -113,40 +113,40 @@ public function testGetVariantsMemoizesNonEmptyCollections(): void
     }
 
     /**
-     * Test that createVariantQuery uses duplicateOf product ID when available
+     * Test that createVariantQuery does not use duplicateOf product ID when available
      */
-    public function testCreateVariantQueryUsesDuplicateOfId(): void
+    public function testCreateVariantQueryDoesNotUseDuplicateOfId(): void
     {
         /** @var ProductFixture $productFixture */
         $productFixture = $this->tester->grabFixture('products');
         $originalProduct = $productFixture->getElement('rad-hoodie');
         self::assertNotNull($originalProduct);
-        
+
         // Create a duplicate product
         $duplicateProduct = new Product();
         $duplicateProduct->id = 999998;
         $duplicateProduct->typeId = $originalProduct->typeId;
         $duplicateProduct->siteId = 1002; // Different site
         $duplicateProduct->duplicateOf = $originalProduct;
-        
+
         // Use reflection to access private createVariantQuery method
         $reflection = new ReflectionClass(Product::class);
         $method = $reflection->getMethod('createVariantQuery');
         $method->setAccessible(true);
-        
+
         /** @var VariantQuery $query */
         $query = $method->invoke(null, $duplicateProduct);
-        
+
         // Use reflection to check the query's ownerId and siteId
         $queryReflection = new ReflectionClass($query);
         $ownerIdProperty = $queryReflection->getProperty('ownerId');
         $ownerIdProperty->setAccessible(true);
         $siteIdProperty = $queryReflection->getProperty('siteId');
         $siteIdProperty->setAccessible(true);
-        
+
         // Should use the original product's ID and siteId
-        self::assertEquals($originalProduct->id, $ownerIdProperty->getValue($query));
-        self::assertEquals($originalProduct->siteId, $siteIdProperty->getValue($query));
+        self::assertNotEquals($originalProduct->id, $ownerIdProperty->getValue($query));
+        self::assertNotEquals($originalProduct->siteId, $siteIdProperty->getValue($query));
     }
 
     /**
@@ -158,25 +158,25 @@ public function testGetVariantsIncludeDisabledParameter(): void
         $productFixture = $this->tester->grabFixture('products');
         $product = $productFixture->getElement('hypercolor-tshirt');
         self::assertNotNull($product);
-        
+
         // Create a disabled variant
         $disabledVariant = new Variant();
         $disabledVariant->title = 'Disabled Variant';
         $disabledVariant->sku = 'disabled-variant-sku';
         $disabledVariant->enabled = false;
         $disabledVariant->setOwner($product);
-        
+
         // Add to product's variants
         $variants = $product->getVariants()->all();
         $variants[] = $disabledVariant;
         $product->setVariants($variants);
-        
+
         // Test without includeDisabled (default)
         $enabledVariants = $product->getVariants(false);
         foreach ($enabledVariants as $variant) {
             self::assertTrue($variant->enabled);
         }
-        
+
         // Test with includeDisabled
         $allVariants = $product->getVariants(true);
         $hasDisabledVariant = false;