diff --git a/externals/mimemailparser/MiddlewareStack.php b/externals/mimemailparser/MiddlewareStack.php
index 3ef6da9349..ecab6445b4 100644
--- a/externals/mimemailparser/MiddlewareStack.php
+++ b/externals/mimemailparser/MiddlewareStack.php
@@ -29,7 +29,7 @@ class MiddlewareStack
      *
      * @param Middleware $middleware
      */
-    public function __construct(MiddleWareContracts $middleware = null)
+    public function __construct(?MiddleWareContracts $middleware = null)
     {
         $this->middleware = $middleware;
     }
diff --git a/externals/mimemailparser/Parser.php b/externals/mimemailparser/Parser.php
index 7f8a1de94d..7c30a6104d 100644
--- a/externals/mimemailparser/Parser.php
+++ b/externals/mimemailparser/Parser.php
@@ -74,7 +74,7 @@ class Parser
      *
      * @param CharsetManager|null $charset
      */
-    public function __construct(CharsetManager $charset = null)
+    public function __construct(?CharsetManager $charset = null)
     {
         if ($charset == null) {
             $charset = new Charset();