fix: warn about missing descriptions and return "" not None

[JoeHCQ1]

This should fix mkdocstrings/mkdocstrings#397 and #137 .

The problem was that empty descriptions were being returned as None in Parameters and Exceptions blocks instead of "".

That None eventually made it to this: https://github.com/mkdocstrings/mkdocstrings/blob/master/src/mkdocstrings/handlers/base.py#L219

And that passed it here: https://github.com/Python-Markdown/markdown/blob/master/markdown/core.py#L225

And later in that function we get a Nonetype error: https://github.com/Python-Markdown/markdown/blob/master/markdown/core.py#L248

Because we also were not recording empty descriptions as errors (which I believe mkdocstrings interprets and reports as warnings) there was nothing to tell the user why python -m mkdocs build had thrown a Nonetype error.

So I:

• Recorded missing descriptions as errors.
• Changed the code to return all missing descriptions as "" instead of None.
• Added test to verify capability.

[pawamoy]

Perfect investigation!

Thanks a lot for taking the time to find and fix the root cause of the issue 🙂

I've made a few suggestions and comments.

[JoeHCQ1]

@pawamoy I am ready for re-review.

[pawamoy]

LGTM!

[pawamoy]

Thanks a lot! Will release it now.

[pawamoy]

Released in 0.16.1