diff --git a/core/modules/system/tests/modules/menu_test/menu_test.routing.yml b/core/modules/system/tests/modules/menu_test/menu_test.routing.yml
index 9cf8f11..2d701dc 100644
--- a/core/modules/system/tests/modules/menu_test/menu_test.routing.yml
+++ b/core/modules/system/tests/modules/menu_test/menu_test.routing.yml
@@ -104,6 +104,6 @@ menu_test_optional_placeholder:
   pattern: '/menu-test/optional/{placeholder}'
   defaults:
     _content: '\Drupal\menu_test\TestControllers::testDefaults'
-    placeholder: ~
+    placeholder: NULL
   requirements:
     _access: 'TRUE'