404 code.

src/Controllers/Controller.php

@@ -104,4 +104,9 @@ abstract class Controller
 
         return $filter;
     }
+
+    protected function pageNotFound() : Response {
+        return (new Response())
+            ->withStatus(404);
+    }
 }

src/Controllers/HtmlController.php

@@ -12,6 +12,7 @@ abstract class HtmlController extends Controller
 {
     protected Twig $twig;
     protected DebugBar $debugBar;
+    protected string $pageNotFoundTemplate = "404.html.twig";
 
     public function __construct(
         Twig $twig,
@@ -57,4 +58,13 @@ abstract class HtmlController extends Controller
 
         return $response;
     }
+
+    protected function pageNotFound(): Response
+    {
+        $response = (parent::pageNotFound());
+        $response->withHeader('Content-Type', 'text/html');
+        $response->getBody()
+                    ->write($this->twig->fetch($this->pageNotFoundTemplate));
+        return $response;
+    }
 }