Google asks a checkout for the sitemaps in its interface.

Here the visible message for all the registered to:
https://www.google.com/webmasters/sitemaps/login

...Create a folder named GOOGLE83915cafghc110o20.html. This folder formally identifies you to Google. You can create this folder in the text publisher of your choice. This folder allows us to check if it is in the same place that your Sitemap, thus it can be empty. We don't look the content. For more information about this folder, click on this link...

Therefore we reviewed the Referencing page so that you can freely add this folder.