diff --git a/src/TranslationLoaderManager.php b/src/TranslationLoaderManager.php
index 08a220e..6715977 100644
--- a/src/TranslationLoaderManager.php
+++ b/src/TranslationLoaderManager.php
@@ -46,7 +46,7 @@ public function load($locale, $group, $namespace = null): array
     protected function getTranslationsForTranslationLoaders(
         string $locale,
         string $group,
-        string $namespace = null
+        ?string $namespace = null
     ): array {
         return collect(config('translation-loader.translation_loaders'))
             ->map(function (string $className) {