diff --git a/src/FirebaseProjectManager.php b/src/FirebaseProjectManager.php
index 2081d14..825f3d5 100644
--- a/src/FirebaseProjectManager.php
+++ b/src/FirebaseProjectManager.php
@@ -25,7 +25,7 @@ public function __construct(Container $app)
         $this->app = $app;
     }
 
-    public function project(string $name = null): FirebaseProject
+    public function project(?string $name = null): FirebaseProject
     {
         $name = $name ?? $this->getDefaultProject();
 
diff --git a/tests/FirebaseProjectManagerTest.php b/tests/FirebaseProjectManagerTest.php
index 9669541..f3e642b 100644
--- a/tests/FirebaseProjectManagerTest.php
+++ b/tests/FirebaseProjectManagerTest.php
@@ -289,7 +289,7 @@ public function it_uses_the_laravel_cache_as_auth_token_cache(): void
         $this->assertInstanceOf(CacheItemPoolInterface::class, $property->getValue($factory));
     }
 
-    private function factoryForProject(string $project = null): Factory
+    private function factoryForProject(?string $project = null): Factory
     {
         $project = $this->app->make(FirebaseProjectManager::class)->project($project);