diff --git a/helpers.php b/helpers.php
index 71b9d2a..60f8929 100644
--- a/helpers.php
+++ b/helpers.php
@@ -10,7 +10,7 @@
      *
      * @return string|bool
      */
-    function laravel_version(string $version = null) {
+    function laravel_version(?string $version = null) {
         $appVersion = app()->version();
 
         if (is_null($version)) {