Where did that Contoso dummy content come from?

HERE'S A THING ... an internal client of mine was working on a modern Experience site, and some of her navigation links were taking her to a page of dummy Contoso content. Like this:

Trying to Google for things like "Contoso content" was no help at all ... so I needed to figure this out by myself.

I wondered if there was a dummy or template page lurking in the SitePages library of the site, but I couldn't see anything. When I looked at the URL in the browser address window, I saw a long URL, but no sign of a page name.

https://xxx.sharepoint.com/sites/DataMI/?xsdata=MDV8MDF8fDVjYTA2ZjVhN2MwNjQyMWYzMDcxMDhkYjA0MzAwZDg3fGNlNTZmYWU2MDU1ZDRjOWZiNmM5OWQzNDE1MDZhNDkxfDB8MHw2MzgxMDgzNzY2MzQ5NjIwMzN8VW5rbm93bnxWR1ZoYlhOVFpXTjFjbWwwZVZObGNuWnBZMlY4ZXlKV0lqb2lNQzR3TGpBd01EQWlMQ0pRSWpvaVYybHVNeklpTENKQlRpSTZJazkwYUdWeUlpd2lWMVFpT2pFeGZRPT18MXxNVFkzTlRJME1EZzJNamN3T1RzeE5qYzFNa

(I've trimmed off several lines of this for space-saving.)

So I started nosing around in the navigation links and found that the links that produced this behaviour were simply pointing at the top level of the site:

https://xxx.sharepoint.com/sites/DataMI/

... with or without the closing slash.

Of course, in a Modern Experience site, you can't have a navigation link that doesn't have a URL ... so I switched those links to labels, which solved the problem temporarily.

If I pasted the URL of the actual Home page into the browser address window, I got the actual home page:

https://xxx.sharepoint.com/sites/DataMI/SitePages/Home.aspx

And if I clicked on the Home link in the top navigation menu, I also got the Home page.

... but no great surprise, as this also had the full link to Home.aspx.

I began wondering if this was something to do with the setting of the default page for the site. So on a hunch, I found Home.aspx in the SitePages library and set it as the site default page.

Problem solved.

All I can think of is that at some time in the site's past, someone either deleted the default page (I don't know how, as SharePoint won't let you delete a designated default page) or found some way to NOT have a default page at all. The fact that the Home navigation link had the full URL of the Home page tends to support both those ideas.

Anyway, if you see this behaviour, now you know why.

I hope this helps someone.