Fix parent field for StockItemSerializer (#11573)

* Fix parent field for StockItemSerializer

- Closes https://github.com/inventree/InvenTree/issues/11507

* Bump API version

src/backend/InvenTree/InvenTree/api_version.py

@@ -1,11 +1,14 @@
 """InvenTree API version information."""
 
 # InvenTree API version
-INVENTREE_API_VERSION = 466
+INVENTREE_API_VERSION = 467
 """Increment this API version number whenever there is a significant change to the API that any clients need to know about."""
 
 INVENTREE_API_TEXT = """
 
+v467 -> 2026-03-20 : https://github.com/inventree/InvenTree/pull/11573
+    - Fix definition for the "parent" field on the StockItemSerializer
+
 v466 -> 2026-03-17 : https://github.com/inventree/InvenTree/pull/11525
     - SalesOrderShipmentComplete endpoint now returns a task ID which can be used to track the progress of the shipment completion process
 

src/backend/InvenTree/stock/serializers.py

@@ -413,6 +413,8 @@ class StockItemSerializer(
     parent = serializers.PrimaryKeyRelatedField(
         many=False,
         read_only=True,
+        required=False,
+        allow_null=True,
         label=_('Parent Item'),
         help_text=_('Parent stock item'),
     )