Fix TypeError when nav is generated automatically

[gferon]

if nav is not specified in mkdocs.yml, the entire on_config function body is skipped but on_serve relies on self.originalDocsDir.

[emmaindal]

Thanks for your contribution @gferon, I've added a comment just to understand the use case a bit more!

[emmaindal]

I'm interested in knowing more about the use case for this. The way I understand it is that the !import statements needs to be configured in the 'nav'. So if you do not have a nav, its almost like we don't want to do anything and bubble some feedback up to the user that a nav is required to use this plugin?

[gferon]

We use Backstage, which makes our mkdocs depend on mkdocs-tech-core.

Some pages were added to our documentation without properly editing the navigation. After reading the documentation of mkdocs, I discovered that if you omit nav, (quoting the doc) it will contain an alphanumerically sorted, nested list of all the Markdown files found within the docs_dir and its sub-directories, which is ideal for us.

Upon removing nav, running mkdocs serve failed, which made me submit this fix 😄

EDIT: maybe it would be more clear if I added a test?

[emmaindal]

@gferon Understand, it makes sense to me! Thanks for giving a bit more context. If you can add a test that would be great!

[camilaibs]

Hi @gferon, just for follow-up, want to add tests? Thanks in advance 🙂

[gferon]

Thanks for reminding me! I had a quick look, and I'm actually not sure how I could easily add a bats test because the bug only affects mkdocs serve and per my understanding, most tests verify that docs can be built using mkdocs build.

[emmaindal]

Do you think we can implement some unittests? just to test the on_confg? I found some examples for the search plugin https://github.com/mkdocs/mkdocs/blob/master/mkdocs/tests/search_tests.py#L208.

[camilaibs]

Hi @gferon 👋🏻 ,
Thanks again for contributing!
I would like to ask if you had time to take a look at Emma's example here.
Would you still like to add tests? Tell us what your plan is, no pressure, just follow along 🙌🏻

[richardmcsong]

I found this PR because I ran into this exact use case! Anything I can do to help with this?

[gferon]

I'll close this PR since it looks like it'll get taken care of with #69