Do not assume request URL is a string. It might be None.

This may happen on layer setup in tests if request was not initialized already properly.
Also check if there is a request at all.

plone/app/caching/purge.py

@@ -282,7 +282,9 @@ def purgeOnModified(object, event):
 def purgeOnMovedOrRemoved(object, event):
     request = getRequest()
     confirmed_delete = (
-        'delete_confirmation' in request.URL
+        request
+        and request.URL is not None
+        and 'delete_confirmation' in request.URL
         and request.REQUEST_METHOD == 'POST'
         and 'form.submitted' in request.form
     )