Fixes: #88, invalid nullable services injection

Signed-off-by: zio-mitch <[email protected]>

Author: zio-mitch

docs/book/v5/tutorials/create-book-module.md

@@ -542,8 +542,8 @@ class BookHandler extends AbstractHandler implements RequestHandlerInterface
         "config"
     )]
     public function __construct(
-        protected HalResponseFactory $responseFactory,
-        protected ResourceGenerator $resourceGenerator,
+        protected ?HalResponseFactory $responseFactory,
+        protected ?ResourceGenerator $resourceGenerator,
         protected BookServiceInterface $bookService,
         protected array $config
     ) {