fix: guard null writes in SessionDriver::setSessionKey

src/Drivers/SessionDriver.php

@@ -37,8 +37,13 @@ public function setSessionKey(string $sessionKey): void
         $this->itemsKey = $sessionKey . '_cart_items';
         $this->conditionsKey = $sessionKey . '_cart_conditions';
 
-        $this->session->put($this->itemsKey, $items);
-        $this->session->put($this->conditionsKey, $conditions);
+        if ($items !== null) {
+            $this->session->put($this->itemsKey, $items);
+        }
+
+        if ($conditions !== null) {
+            $this->session->put($this->conditionsKey, $conditions);
+        }
     }
 
     public function getDriverName(): string

tests/Unit/Drivers/SessionDriverTest.php

@@ -70,4 +70,15 @@
     test('getSessionModel returns null', function () {
         expect($this->driver->getSessionModel())->toBeNull();
     });
+
+    test('setSessionKey on empty cart does not write null to session', function () {
+        $this->driver->setSessionKey('new-key');
+
+        // After key change, empty cart should still return empty arrays, not null
+        expect($this->driver->getItems())->toBe([]);
+        expect($this->driver->getConditions())->toBe([]);
+        // And the session should not have null values written
+        expect($this->session->get('new-key_cart_items'))->toBeNull();
+        expect($this->session->get('new-key_cart_conditions'))->toBeNull();
+    });
 });