diff --git a/Models/NullTask.php b/Models/NullTask.php
index 1b4732d..99e7fc3 100755
--- a/Models/NullTask.php
+++ b/Models/NullTask.php
@@ -44,4 +44,12 @@ final class NullTask extends Task
     {
         return ['id' => $this->id];
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function jsonSerialize() : mixed
+    {
+        return ['id' => $this->id];
+    }
 }
diff --git a/Models/NullTaskElement.php b/Models/NullTaskElement.php
index c3f472f..a9bd20c 100755
--- a/Models/NullTaskElement.php
+++ b/Models/NullTaskElement.php
@@ -36,4 +36,12 @@ final class NullTaskElement extends TaskElement
         $this->id = $id;
         parent::__construct();
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function jsonSerialize() : mixed
+    {
+        return ['id' => $this->id];
+    }
 }