diff --git a/Models/NullSurveyTemplate.php b/Models/NullSurveyTemplate.php
index 7ec4227..982f4c6 100755
--- a/Models/NullSurveyTemplate.php
+++ b/Models/NullSurveyTemplate.php
@@ -36,4 +36,12 @@ final class NullSurveyTemplate extends SurveyTemplate
         $this->id = $id;
         parent::__construct();
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function jsonSerialize() : mixed
+    {
+        return ['id' => $this->id];
+    }
 }
diff --git a/Models/NullSurveyTemplateElement.php b/Models/NullSurveyTemplateElement.php
index 63f1432..eb38b33 100755
--- a/Models/NullSurveyTemplateElement.php
+++ b/Models/NullSurveyTemplateElement.php
@@ -35,4 +35,12 @@ final class NullSurveyTemplateElement extends SurveyTemplateElement
     {
         $this->id = $id;
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function jsonSerialize() : mixed
+    {
+        return ['id' => $this->id];
+    }
 }
diff --git a/Models/NullSurveyTemplateElementL11n.php b/Models/NullSurveyTemplateElementL11n.php
index efbbd65..43dc26a 100755
--- a/Models/NullSurveyTemplateElementL11n.php
+++ b/Models/NullSurveyTemplateElementL11n.php
@@ -36,4 +36,12 @@ final class NullSurveyTemplateElementL11n extends SurveyTemplateElementL11n
         $this->id = $id;
         parent::__construct();
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function jsonSerialize() : mixed
+    {
+        return ['id' => $this->id];
+    }
 }
diff --git a/Models/NullSurveyTemplateL11n.php b/Models/NullSurveyTemplateL11n.php
index 474bc6d..c090a7a 100755
--- a/Models/NullSurveyTemplateL11n.php
+++ b/Models/NullSurveyTemplateL11n.php
@@ -36,4 +36,12 @@ final class NullSurveyTemplateL11n extends SurveyTemplateL11n
         $this->id = $id;
         parent::__construct();
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function jsonSerialize() : mixed
+    {
+        return ['id' => $this->id];
+    }
 }
diff --git a/Models/NullSurveyTemplateLabelL11n.php b/Models/NullSurveyTemplateLabelL11n.php
index ba7d043..32d8bd2 100755
--- a/Models/NullSurveyTemplateLabelL11n.php
+++ b/Models/NullSurveyTemplateLabelL11n.php
@@ -36,4 +36,12 @@ final class NullSurveyTemplateLabelL11n extends SurveyTemplateLabelL11n
         $this->id = $id;
         parent::__construct();
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function jsonSerialize() : mixed
+    {
+        return ['id' => $this->id];
+    }
 }