return an error message when item not found instead of empty object

app/Http/Controllers/ItemController.php

@@ -46,7 +46,7 @@ class ItemController extends Controller
             Log::error($exception->getMessage());
             Log::error($exception->getTraceAsString());
             return response()->json([
-                'item' => [],
+                'error' => 'Item not found.',
             ], Response::HTTP_NOT_FOUND);
         }
     }