I've noticed a bunch of projects recently (mostly with a single openSUSE package mapping) that have no way to check versions. For example, https://release-monitoring.org/project/381934/ has a custom backend but the update URL is empty. The status message for this project says "Could not call : "None" of "snobol4", with error: argument of type 'NoneType' is not iterable" because there's no URL to check.

Anitya should disallow creating projects with no way to check versions. The point of a project in Anitya is to look for new versions, after all, so it's pointless to create a project where that's not possible.