[tag:bug]

Questions which do not have any tags associated with any languages do not get their code blocks automatically highlighted at all. Examples:

https://stackoverflow.com/questions/61112840/preloader-is-not-working-on-angular-universal-ssr-app

https://stackoverflow.com/questions/63197222/how-to-get-a-list-of-members-in-a-guild-discord-js

Note that questions *will* get highlighted if they have at least one tag with a "Highlight Language" in their wiki, *even if that language is `default`* - like with [regex](https://stackoverflow.com/tags/regex/info). Questions with at least one such tag will get their code blocks automatically highlighted. In contrast, a question only with tags like [discord.js](https://stackoverflow.com/tags/discord.js/info) which has no highlight language (not even `default`) will not have any code blocks highlighted.

I think when no tags have languages associated with them, the question's code blocks should be highlighted automatically. Maybe remove the difference between the association with `default` highlighting a non-existing language association while you're at it, unless it's needed for something. (Or give *all* tags a `default` language association.)

All questions should at least have something like

```html
<div style="display:none" id="js-codeblock-lang">default</div>
```

but it should never be empty, or auto-highlighting won't work:

```html
<div style="display:none" id="js-codeblock-lang"></div>
```

This issue is pretty similar to a related standalone question: [Improving syntax highlighting language auto-detection](https://meta.stackexchange.com/q/354793).