diff --git a/Models/NullComment.php b/Models/NullComment.php
new file mode 100644
index 0000000..65db2ce
--- /dev/null
+++ b/Models/NullComment.php
@@ -0,0 +1,38 @@
+<?php
+/**
+ * Orange Management
+ *
+ * PHP Version 7.4
+ *
+ * @package   Modules\Comment\Models
+ * @copyright Dennis Eichhorn
+ * @license   OMS License 1.0
+ * @version   1.0.0
+ * @link      https://orange-management.org
+ */
+declare(strict_types=1);
+
+namespace Modules\Comments\Models;
+
+/**
+ * Null model
+ *
+ * @package Modules\Comment\Models
+ * @license OMS License 1.0
+ * @link    https://orange-management.org
+ * @since   1.0.0
+ */
+final class NullComment extends Comment
+{
+    /**
+     * Constructor
+     *
+     * @param int $id Model id
+     *
+     * @since 1.0.0
+     */
+    public function __construct(int $id = 0)
+    {
+        $this->id = $id;
+    }
+}
diff --git a/tests/Models/CommentMapperTest.php b/tests/Models/CommentMapperTest.php
index 099a638..ec5d987 100644
--- a/tests/Models/CommentMapperTest.php
+++ b/tests/Models/CommentMapperTest.php
@@ -17,6 +17,7 @@ namespace Modules\Comments\tests\Models;
 use Modules\Admin\Models\NullAccount;
 use Modules\Comments\Models\Comment;
 use Modules\Comments\Models\CommentMapper;
+use Phan\Language\Element\Comment\NullComment;
 
 /**
  * @internal
@@ -29,7 +30,7 @@ class CommentMapperTest extends \PHPUnit\Framework\TestCase
         $comment->setCreatedBy(new NullAccount(1));
         $comment->setTitle('Test Title');
         $comment->setContent('Test Content');
-        $comment->setRef(1);
+        $comment->setRef(null);
         $comment->setList(1);
 
         $id = CommentMapper::create($comment);
diff --git a/tests/Models/CommentTest.php b/tests/Models/CommentTest.php
index 6c42436..8a9193d 100644
--- a/tests/Models/CommentTest.php
+++ b/tests/Models/CommentTest.php
@@ -16,6 +16,7 @@ namespace Modules\Comments\tests\Models;
 
 use Modules\Admin\Models\NullAccount;
 use Modules\Comments\Models\Comment;
+use Modules\Comments\Models\NullComment;
 
 /**
  * @internal
@@ -46,8 +47,8 @@ class CommentTest extends \PHPUnit\Framework\TestCase
         $comment->setList(2);
         self::assertEquals(2, $comment->getList());
 
-        $comment->setRef(3);
-        self::assertEquals(3, $comment->getRef());
+        $comment->setRef(new NullComment(3));
+        self::assertEquals(3, $comment->getRef()->getId());
 
         $comment->setTitle('Test Title');
         self::assertEquals('Test Title', $comment->getTitle());