[BUGFIX] Always send strings to the method createStream

PHP8.1 throws an TypeError if we sending null to createStream

Resolves: #98417
Releases: main, 11.5
Change-Id: I327751c2cb13991122c84f4333a4976b9d0a0dae
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75878
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>

typo3/sysext/extbase/Classes/Mvc/Controller/ActionController.php

@@ -1089,7 +1089,7 @@ protected function htmlResponse(string $html = null): ResponseInterface
     {
         return $this->responseFactory->createResponse()
             ->withHeader('Content-Type', 'text/html; charset=utf-8')
-            ->withBody($this->streamFactory->createStream($html ?? $this->view->render()));
+            ->withBody($this->streamFactory->createStream((string)($html ?? $this->view->render())));
     }
 
     /**
@@ -1103,6 +1103,6 @@ protected function jsonResponse(string $json = null): ResponseInterface
     {
         return $this->responseFactory->createResponse()
             ->withHeader('Content-Type', 'application/json; charset=utf-8')
-            ->withBody($this->streamFactory->createStream($json ?? $this->view->render()));
+            ->withBody($this->streamFactory->createStream((string)($json ?? $this->view->render())));
     }
 }