diff --git a/src/PHPCR/Shell/Config/ConfigManager.php b/src/PHPCR/Shell/Config/ConfigManager.php
index b74638f..0ca4aa9 100644
--- a/src/PHPCR/Shell/Config/ConfigManager.php
+++ b/src/PHPCR/Shell/Config/ConfigManager.php
@@ -60,7 +60,7 @@ class ConfigManager
      * @param QuestionHelper|DialogHelper $questionHelper
      * @param Filesystem                  $filesystem
      */
-    public function __construct($questionHelper, Filesystem $filesystem = null)
+    public function __construct($questionHelper, ?Filesystem $filesystem = null)
     {
         if (null === $filesystem) {
             $filesystem = new Filesystem();
@@ -174,7 +174,7 @@ public function getPhpcrshConfig()
     /**
      * Initialize a configuration files.
      */
-    public function initConfig(OutputInterface $output = null)
+    public function initConfig(?OutputInterface $output = null)
     {
         $log = function ($message) use ($output) {
             if ($output) {
diff --git a/src/PHPCR/Shell/Config/ProfileLoader.php b/src/PHPCR/Shell/Config/ProfileLoader.php
index a9802e2..869505e 100644
--- a/src/PHPCR/Shell/Config/ProfileLoader.php
+++ b/src/PHPCR/Shell/Config/ProfileLoader.php
@@ -24,7 +24,7 @@ class ProfileLoader
     protected $config;
     protected $filesystem;
 
-    public function __construct(ConfigManager $config, Filesystem $filesystem = null)
+    public function __construct(ConfigManager $config, ?Filesystem $filesystem = null)
     {
         $this->config = $config;
         $this->filesystem = $filesystem ?: new Filesystem();
diff --git a/src/PHPCR/Shell/Console/Command/BaseCommand.php b/src/PHPCR/Shell/Console/Command/BaseCommand.php
index 3e43b99..8e67e75 100644
--- a/src/PHPCR/Shell/Console/Command/BaseCommand.php
+++ b/src/PHPCR/Shell/Console/Command/BaseCommand.php
@@ -23,7 +23,7 @@ class BaseCommand extends Command implements ContainerAwareInterface
      */
     private $container;
 
-    public function setContainer(ContainerInterface $container = null): void
+    public function setContainer(?ContainerInterface $container = null): void
     {
         $this->container = $container;
     }
diff --git a/src/PHPCR/Shell/Test/ApplicationTester.php b/src/PHPCR/Shell/Test/ApplicationTester.php
index 2d508ea..153b0ba 100644
--- a/src/PHPCR/Shell/Test/ApplicationTester.php
+++ b/src/PHPCR/Shell/Test/ApplicationTester.php
@@ -43,7 +43,7 @@ class ApplicationTester
      *
      * @param Application $application An Application instance to test.
      */
-    public function __construct(Application $application, ShellApplication $shellApplication = null)
+    public function __construct(Application $application, ?ShellApplication $shellApplication = null)
     {
         $this->output = new StreamOutput(fopen('php://memory', 'w', false));