chore: fix phpstan errors

src/Controller/Api/TravelController.php

@@ -58,7 +58,7 @@ class TravelController extends AbstractController
         name: 'api_travel_single_code',
         defaults: ['hotelCode' => null],
     )]
-    public function byCode(Request $request, $dateCode, ?string $hotelCode = null): JsonResponse
+    public function byCode(Request $request, string $dateCode, ?string $hotelCode = null): JsonResponse
     {
         // sanitize date code by removing potential dividers
         $dateCode = (new DateCodeUtility())->sanitize($dateCode);