Empty string used as taxonomy term breaks taxonomy list page

[mprasil]

Bug Report

Environment

Zola version: 0.16.1

Expected Behavior

I think throwing an error would be most appropriate.

Current Behavior

When adding an empty string instead of proper taxonomy term, Zola renders page for this single term instead of listing all terms.

Step to reproduce

In the page frontmatter add any taxonomy with empty string as term:

+++
title = "Reproduce bug"
[taxonomies]
tag = [""]
+++

Then visit ${baseurl}/tag/ in your browser, you'll see list of articles that are tagged with "" instead of list of tags like one would expect.

I assume this is due to tag named "" being sluggified to empty string which results in conflicting /tag/ path being generated overwriting the file that's normally used for listing all tags.

[mprasil]

I realize, that this is somewhat user error as the empty tag was indeed added to the list of tags, but I think virtually all such cases would not be intentional. (eg. user adding just empty string as placeholder while writing the page, then forgetting to update it)

On top of that, the issue manifests in a place where user is unlikely to check and breaks the site somewhat silently which makes for a nasty issue to spot. It took me a while to notice this and quite a while to figure out what's going on - and that was me actually tinkering with the the page look, so I was actually working on that specific template. Otherwise I can see this going unnoticed for a while. 😅