Object of class Url could not be converted to string

The fix looks great, but I fear we need some form of test coverage here.

+++ b/core/modules/views/src/Plugin/EntityReferenceSelection/ViewsSelection.php
@@ -147,8 +147,8 @@ public function buildConfigurationForm(array $form, FormStateInterface $form_sta
-            '@create' => Url::fromRoute('views_ui.add'),
-            '@existing' => Url::fromRoute('entity.view.collection'),
+            '@create' => Url::fromRoute('views_ui.add')->toString(),
+            '@existing' => Url::fromRoute('entity.view.collection')->toString(),

This is a shame we can't use Url object as a placeholder. I made this mistake a lot of times.

This is a shame we can't use Url object as a placeholder. I made this mistake a lot of times.

It used to work, but if an exception is thrown inside the magic __toString(), good luck!

#2472421: Entity reference, views filter reference method is broken.