diff --git a/Models/NullWikiApp.php b/Models/NullWikiApp.php
index 96353a1..747d1dc 100755
--- a/Models/NullWikiApp.php
+++ b/Models/NullWikiApp.php
@@ -35,4 +35,12 @@ final class NullWikiApp extends WikiApp
     {
         $this->id = $id;
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function jsonSerialize() : mixed
+    {
+        return ['id' => $this->id];
+    }
 }
diff --git a/Models/NullWikiCategory.php b/Models/NullWikiCategory.php
index 2aefc07..440a04e 100755
--- a/Models/NullWikiCategory.php
+++ b/Models/NullWikiCategory.php
@@ -35,4 +35,12 @@ final class NullWikiCategory extends WikiCategory
     {
         $this->id = $id;
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function jsonSerialize() : mixed
+    {
+        return ['id' => $this->id];
+    }
 }
diff --git a/Models/NullWikiDoc.php b/Models/NullWikiDoc.php
index 4ec0a1b..adb4eaf 100755
--- a/Models/NullWikiDoc.php
+++ b/Models/NullWikiDoc.php
@@ -35,4 +35,12 @@ final class NullWikiDoc extends WikiDoc
     {
         $this->id = $id;
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function jsonSerialize() : mixed
+    {
+        return ['id' => $this->id];
+    }
 }
diff --git a/Models/NullWikiDocHistory.php b/Models/NullWikiDocHistory.php
index cf891af..8ffa1ee 100755
--- a/Models/NullWikiDocHistory.php
+++ b/Models/NullWikiDocHistory.php
@@ -35,4 +35,12 @@ final class NullWikiDocHistory extends WikiDocHistory
     {
         $this->id = $id;
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function jsonSerialize() : mixed
+    {
+        return ['id' => $this->id];
+    }
 }