diff --git a/src/Server/Response.php b/src/Server/Response.php
index 59695dc..c4c07d2 100644
--- a/src/Server/Response.php
+++ b/src/Server/Response.php
@@ -123,7 +123,7 @@ public function removeHeader(string $name): static
      *
      * @return mixed
      */
-    public function getHeader(string $name = null): mixed
+    public function getHeader(null|string $name = null): mixed
     {
         if (!$name) {
             return $this->headers;