mkdocs build fails when the tags plugin is present but the tags_file attribute is missing

[ben519]

Contribution guidelines

• I've read the contribution guidelines and wholeheartedly agree

I've found a bug and checked that ...

• ... the problem doesn't occur with the mkdocs or readthedocs themes
• ... the problem persists when all overrides are removed, i.e. custom_dir, extra_javascript and extra_css
• ... the documentation does not mention anything about my problem
• ... there are no open or closed issues that are related to my problem

Description

According to the docs, I should be able to include the tags plugin without also including a tags_file. This worked until recently when I encountered an error running mkdocs build.

Expected behaviour

mkdocs build should render the site even if tags_file is excluded.

Actual behaviour

mkdocs.yml

...

plugins:
  - tags

error

(venv) bgorman@Bens-MacBook-Pro practice-probs % python3 -m mkdocs build
INFO     -  Cleaning site directory
INFO     -  Building documentation to directory: /Users/bgorman/Dropbox (GormAnalysis)/Practice Probs/practice-probs/site
Traceback (most recent call last):
  File "/usr/local/Cellar/python@3.9/3.9.13_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/local/Cellar/python@3.9/3.9.13_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/Users/bgorman/Dropbox (GormAnalysis)/Practice Probs/practice-probs/venv/lib/python3.9/site-packages/mkdocs/__main__.py", line 236, in <module>
    cli()
  File "/Users/bgorman/Dropbox (GormAnalysis)/Practice Probs/practice-probs/venv/lib/python3.9/site-packages/click/core.py", line 1130, in __call__
    return self.main(*args, **kwargs)
  File "/Users/bgorman/Dropbox (GormAnalysis)/Practice Probs/practice-probs/venv/lib/python3.9/site-packages/click/core.py", line 1055, in main
    rv = self.invoke(ctx)
  File "/Users/bgorman/Dropbox (GormAnalysis)/Practice Probs/practice-probs/venv/lib/python3.9/site-packages/click/core.py", line 1657, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Users/bgorman/Dropbox (GormAnalysis)/Practice Probs/practice-probs/venv/lib/python3.9/site-packages/click/core.py", line 1404, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/bgorman/Dropbox (GormAnalysis)/Practice Probs/practice-probs/venv/lib/python3.9/site-packages/click/core.py", line 760, in invoke
    return __callback(*args, **kwargs)
  File "/Users/bgorman/Dropbox (GormAnalysis)/Practice Probs/practice-probs/venv/lib/python3.9/site-packages/mkdocs/__main__.py", line 192, in build_command
    build.build(config.load_config(**kwargs), dirty=not clean)
  File "/Users/bgorman/Dropbox (GormAnalysis)/Practice Probs/practice-probs/venv/lib/python3.9/site-packages/mkdocs/commands/build.py", line 287, in build
    nav = config['plugins'].run_event('nav', nav, config=config, files=files)
  File "/Users/bgorman/Dropbox (GormAnalysis)/Practice Probs/practice-probs/venv/lib/python3.9/site-packages/mkdocs/plugins.py", line 102, in run_event
    result = method(item, **kwargs)
  File "/Users/bgorman/Dropbox (GormAnalysis)/Practice Probs/practice-probs/venv/lib/python3.9/site-packages/material/plugins/tags/plugin.py", line 70, in on_nav
    self.tags_file = self._get_tags_file(files, file)
  File "/Users/bgorman/Dropbox (GormAnalysis)/Practice Probs/practice-probs/venv/lib/python3.9/site-packages/material/plugins/tags/plugin.py", line 108, in _get_tags_file
    file = files.get_file_from_path(path)
  File "/Users/bgorman/Dropbox (GormAnalysis)/Practice Probs/practice-probs/venv/lib/python3.9/site-packages/mkdocs/structure/files.py", line 32, in get_file_from_path
    return self.src_paths.get(os.path.normpath(path))
  File "/usr/local/Cellar/python@3.9/3.9.13_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/posixpath.py", line 336, in normpath
    path = os.fspath(path)
TypeError: expected str, bytes or os.PathLike object, not NoneType

Steps to reproduce

1. Stand up a Hello World project
2. Insert the tags plugin inside mkdocs.yml

plugins:
  - tags

3. Attempt to build the site

python3 -m mkdocs build

Package versions

• Python: python --version: Python 3.9.13 (also tested on 3.10)
• MkDocs: mkdocs --version: 1.3.0
• Material: pip show mkdocs-material | grep -E ^Version: Version: 8.3.9+insiders.4.20.0

Configuration

site_name: Hello World

theme:
  name: material
 
plugins:
  - tags

nav:
  - Home: index.md

System information

• Operating system: Mac OS 12.4
• Browser: Chrome Version 103.0.5060.114 (Official Build) (x86_64)

[squidfunk]

Thanks for reporting. That was a 4.20.0 regression, sorry for the inconvenience.

Fixed in squidfunk/mkdocs-material-insiders@9083945

[squidfunk]

Released as part of 8.3.9+insiders-4.20.1.