diff --git a/Classes/Controller/AbstractController.php b/Classes/Controller/AbstractController.php
index bb494ec..a5884da 100644
--- a/Classes/Controller/AbstractController.php
+++ b/Classes/Controller/AbstractController.php
@@ -118,7 +118,7 @@ protected function buildPagination(Query $query, int $currentPage): void
      *
      * @param string|null $html
      */
-    protected function htmlResponseCompatibility(string $html = null)
+    protected function htmlResponseCompatibility(?string $html = null)
     {
         return $this->responseFactory->createResponse()
             ->withHeader('Content-Type', 'text/html; charset=utf-8')