IcingaZone: render parent zone names

library/Director/Objects/IcingaZone.php

@@ -12,4 +12,9 @@ class IcingaZone extends IcingaObject
         'object_type'    => null,
         'parent_zone_id' => null,
     );
+
+    protected function renderParent_zone_id()
+    {
+        return $this->renderZoneProperty('parent_zone', $this->parent_zone_id)
+    }
 }