diff --git a/Model/Client.php b/Model/Client.php
index 356ac6d5..91f14bb1 100644
--- a/Model/Client.php
+++ b/Model/Client.php
@@ -24,14 +24,14 @@ class Client implements ClientInterface
     protected $id;
 
     /**
-     * @var string
+     * @var string|null
      */
-    protected string $randomId;
+    protected ?string $randomId = null;
 
     /**
-     * @var string
+     * @var string|null
      */
-    protected string $secret;
+    protected ?string $secret = null;
 
     /**
      * @var array
@@ -59,7 +59,7 @@ public function getId()
     /**
      * {@inheritdoc}
      */
-    public function setRandomId($random)
+    public function setRandomId( string $random )
     {
         $this->randomId = $random;
     }
@@ -67,7 +67,7 @@ public function setRandomId($random)
     /**
      * {@inheritdoc}
      */
-    public function getRandomId(): string
+    public function getRandomId(): ?string
     {
         return $this->randomId;
     }
@@ -91,7 +91,7 @@ public function setSecret($secret)
     /**
      * {@inheritdoc}
      */
-    public function getSecret(): string
+    public function getSecret(): ?string
     {
         return $this->secret;
     }
diff --git a/Security/Authentication/Token/OAuthToken.php b/Security/Authentication/Token/OAuthToken.php
index 2e5979ce..9d00b0d0 100644
--- a/Security/Authentication/Token/OAuthToken.php
+++ b/Security/Authentication/Token/OAuthToken.php
@@ -25,19 +25,19 @@ class OAuthToken extends AbstractToken
     /**
      * @var string
      */
-    protected $token;
+    protected string $token;
 
-    public function setToken($token)
+    public function setToken(string $token)
     {
         $this->token = $token;
     }
 
-    public function getToken()
+    public function getToken(): string
     {
         return $this->token;
     }
 
-    public function getCredentials()
+    public function getCredentials(): string
     {
         return $this->token;
     }
diff --git a/Storage/OAuthStorage.php b/Storage/OAuthStorage.php
index 6bf5af03..78760493 100644
--- a/Storage/OAuthStorage.php
+++ b/Storage/OAuthStorage.php
@@ -58,14 +58,14 @@ class OAuthStorage implements IOAuth2RefreshTokens, IOAuth2GrantUser, IOAuth2Gra
     protected AuthCodeManagerInterface $authCodeManager;
 
     /**
-     * @var UserProviderInterface
+     * @var UserProviderInterface|null
      */
-    protected UserProviderInterface $userProvider;
+    protected ?UserProviderInterface $userProvider;
 
     /**
-     * @var PasswordHasherFactoryInterface
+     * @var PasswordHasherFactoryInterface|null
      */
-    protected PasswordHasherFactoryInterface $passwordHasherFactory;
+    protected ?PasswordHasherFactoryInterface $passwordHasherFactory;
 
     /**
      * @var array [uri] => GrantExtensionInterface