diff --git a/Models/NullNewsArticle.php b/Models/NullNewsArticle.php
index c0b95f9..b4d3ae8 100755
--- a/Models/NullNewsArticle.php
+++ b/Models/NullNewsArticle.php
@@ -36,4 +36,12 @@ final class NullNewsArticle extends NewsArticle
         $this->id = $id;
         parent::__construct();
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function jsonSerialize() : mixed
+    {
+        return ['id' => $this->id];
+    }
 }
diff --git a/Models/NullNewsSeen.php b/Models/NullNewsSeen.php
index be346ac..e81175f 100755
--- a/Models/NullNewsSeen.php
+++ b/Models/NullNewsSeen.php
@@ -36,4 +36,12 @@ final class NullNewsSeen extends NewsSeen
         $this->id = $id;
         parent::__construct();
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function jsonSerialize() : mixed
+    {
+        return ['id' => $this->id];
+    }
 }