What does /null appended to the URL mean in Google Analytics

Question

For some reason, we're having this report in Analytics where /null is getting added to the URLs like /this-is-a-page/null. Something to note is that when I go to the page and added something in the URL segment, it goes to a 404 page which is correct. When I add /null, the page just refreshes.

I can't for the life of me figure out what is causing this and I was wondering if anyone here knows what is causing this and probably a solution on how to solve it?

Thanks!