IcingaObject(Legacy): Render legacy customvars

refs #12919

library/Director/Objects/IcingaObject.php

@@ -1851,6 +1851,18 @@ abstract class IcingaObject extends DbObject implements IcingaConfigRenderer
         }
     }
 
+    /**
+     * @return string
+     */
+    protected function renderLegacyCustomVars()
+    {
+        if ($this->supportsCustomVars()) {
+            return $this->vars()->toLegacyConfigString();
+        } else {
+            return '';
+        }
+    }
+
     /**
      * @return string
      */
@@ -2024,7 +2036,7 @@ abstract class IcingaObject extends DbObject implements IcingaConfigRenderer
             $this->renderLegacyGroups(),
             //$this->renderMultiRelations(),
             //$this->renderCustomExtensions(),
-            //$this->renderCustomVars(),
+            $this->renderLegacyCustomVars(),
             $this->renderLegacySuffix()
         ));