diff --git a/src/LaravelPhpRdKafkaServiceProvider.php b/src/LaravelPhpRdKafkaServiceProvider.php
index d0525b8..d73b1f8 100644
--- a/src/LaravelPhpRdKafkaServiceProvider.php
+++ b/src/LaravelPhpRdKafkaServiceProvider.php
@@ -29,7 +29,7 @@ public function boot(): void
         }
     }
 
-    protected function packageBasePath(string $directory = null): string
+    protected function packageBasePath(?string $directory = null): string
     {
         if ($directory === null) {
             return __DIR__;