Resolve "Uncaught ValueError when tags are not pulled into local repository"

Description

Adds special casing for git repositories that don't have tags - this resolves an unhelpful crash for users who managed to acquire such a repository.

Currently this isn't tested; I can't really see how we would test it, either, since it requires that the user clones their repository without tags.

This merge request, when approved, will close issue/bug: #380 (closed)