diff --git a/Models/NullSession.php b/Models/NullSession.php
index b0c21ee..2e08376 100755
--- a/Models/NullSession.php
+++ b/Models/NullSession.php
@@ -36,4 +36,12 @@ final class NullSession extends Session
         $this->id = $id;
         parent::__construct();
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function jsonSerialize() : mixed
+    {
+        return ['id' => $this->id];
+    }
 }
diff --git a/Models/NullSessionElement.php b/Models/NullSessionElement.php
index ad84c39..0769365 100755
--- a/Models/NullSessionElement.php
+++ b/Models/NullSessionElement.php
@@ -36,4 +36,12 @@ final class NullSessionElement extends SessionElement
         $this->id = $id;
         parent::__construct();
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function jsonSerialize() : mixed
+    {
+        return ['id' => $this->id];
+    }
 }