diff --git a/src/AuthContext.php b/src/AuthContext.php
index a2774121..14ec2408 100644
--- a/src/AuthContext.php
+++ b/src/AuthContext.php
@@ -21,7 +21,7 @@ public function __construct(
     ) {
     }
 
-    public function start(TokenInterface $token, string $transport = null): void
+    public function start(TokenInterface $token, ?string $transport = null): void
     {
         $this->closed = false;
         $this->actor = null;
diff --git a/src/AuthContextInterface.php b/src/AuthContextInterface.php
index bc7d893b..645327ab 100644
--- a/src/AuthContextInterface.php
+++ b/src/AuthContextInterface.php
@@ -12,7 +12,7 @@ interface AuthContextInterface
     /**
      * Start new auth context based on a given token. Actor can be received on demand.
      */
-    public function start(TokenInterface $token, string $transport = null): void;
+    public function start(TokenInterface $token, ?string $transport = null): void;
 
     /**
      * Returns associated token if any.
diff --git a/src/TokenStorageInterface.php b/src/TokenStorageInterface.php
index de823dae..62e027d6 100644
--- a/src/TokenStorageInterface.php
+++ b/src/TokenStorageInterface.php
@@ -21,11 +21,9 @@ public function load(string $id): ?TokenInterface;
     /**
      * Create token based on the payload provided by actor provider.
      *
-     * @param \DateTimeInterface|null $expiresAt
-     *
      * @throws TokenStorageException
      */
-    public function create(array $payload, \DateTimeInterface $expiresAt = null): TokenInterface;
+    public function create(array $payload, ?\DateTimeInterface $expiresAt = null): TokenInterface;
 
     /**
      * Delete token from the persistent storage.
diff --git a/tests/Stub/TestAuthToken.php b/tests/Stub/TestAuthToken.php
index de8b2f2f..99f2c4c5 100644
--- a/tests/Stub/TestAuthToken.php
+++ b/tests/Stub/TestAuthToken.php
@@ -22,7 +22,7 @@ class TestAuthToken implements TokenInterface
      * @param array                   $payload
      * @param \DateTimeInterface|null $expiresAt
      */
-    public function __construct(string $id, array $payload, \DateTimeInterface $expiresAt = null)
+    public function __construct(string $id, array $payload, ?\DateTimeInterface $expiresAt = null)
     {
         $this->id = $id;
         $this->expiresAt = $expiresAt;