chore: make apis nullable (#7763)

what:

- makes top level attributes of each object an optional field in the http layer where possible

RESOLVES CORE-2229

packages/core/core-flows/src/order/workflows/create-fulfillment.ts

@@ -102,7 +102,8 @@ function prepareFulfillmentData({
     } as FulfillmentWorkflow.CreateFulfillmentItemWorkflowDTO
   })
 
-  let locationId: string | undefined = input.location_id
+  let locationId: string | undefined | null = input.location_id
+
   if (!locationId) {
     locationId = shippingOption.service_zone.fulfillment_set.location?.id
   }

packages/core/core-flows/src/order/workflows/create-return.ts

@@ -168,7 +168,7 @@ function prepareFulfillmentData({
     } as FulfillmentWorkflow.CreateFulfillmentItemWorkflowDTO
   })
 
-  let locationId: string | undefined = input.location_id
+  let locationId: string | undefined | null = input.location_id
   if (!locationId) {
     locationId = returnShippingOption.service_zone.fulfillment_set.location?.id
   }