diff --git a/src/PsyshFacade.php b/src/PsyshFacade.php
index 6b6ff96..8552a38 100644
--- a/src/PsyshFacade.php
+++ b/src/PsyshFacade.php
@@ -48,7 +48,7 @@ public static function debug(array $variables = [], $bind = null): void
         self::$shell::debug(array_merge(self::$shell->getScopeVariables(), $variables), $bind);
     }
 
-    public function setContainer(ContainerInterface $container = null): void
+    public function setContainer(?ContainerInterface $container = null): void
     {
         self::$container = $container;
     }