Fix AttributeError("'NoneType' object has no attribute 'get'") when including TOC

[tomas-pajurek]

When a page includes other page (via .. include::) containing a TOC (.. toctree::), the sphinx-build command fails with following error:

Theme error:
An error happened in rendering the page toc-extension.include.
Reason: AttributeError("'NoneType' object has no attribute 'get'")

Minimal repro can be found here.

I have traced the issue to recursive function add_header_level_recursive which receives None as an argument in the situation described in the repro above.

This MR fixes the issue by not calling add_header_level_recursive function with None argument.

[bollwyvl]

LGTM!

[bollwyvl]

Sure!

[jorisvandenbossche]

@tpajurek-dtml thanks a lot for the fix!

Since you already constructed a minimal repro sphinx site, would you like to add that to our tests? You can add it as a new directory in https://github.com/pydata/pydata-sphinx-theme/tree/master/tests/sites and then add a new test function in https://github.com/pydata/pydata-sphinx-theme/blob/master/tests/test_build.py (and already ensuring it doesn't error might be sufficient)

[tomas-pajurek]

@bollwyvl @jorisvandenbossche Sure, I will include the refactoring as well as the test.

[tomas-pajurek]

It is done.

[bollwyvl]

L(even better)TM!

[jorisvandenbossche]

Thanks for adding the test!
I just pushed a small change before merging this: I simplified the conf.py a bit to the bare content needed for the test (and removed the .gitignore, since in our testing machinery the build output is put in a temporary directory anyway).

[jorisvandenbossche]

And released 0.5.2 with this fix!

[tomas-pajurek]

Great, thanks !