Docutils 0.18 returns an error when searching for author metadata

[choldgraf]

Describe the bug

On a page that has page metadata, but not the metadata needed for ABlog, there seems to be a broken logic check for whether metadata fields exist and we get a list index error:

File "/home/choldgraf/github/forks/python/ebp/pydata-sphinx-theme/.nox/docs-live/lib/python3.9/site-packages/ablog/post.py", line 186, in apply
    metadata["author"] = list(docinfo.traverse(nodes.author))[0].astext()

I think this is because of the check here:

ablog/ablog/post.py

Lines 185 to 191 in 9545dc1

	if docinfo.traverse(nodes.author):
	metadata["author"] = list(docinfo.traverse(nodes.author))[0].astext()
	# These two fields are special-cased in docutils
	if docinfo.traverse(nodes.date):
	metadata["date"] = list(docinfo.traverse(nodes.date))[0].astext()
	if "blogpost" not in metadata and self.env.docname not in self.config.matched_blog_posts:
	return None

I think for some reason traverse(nodes.author) will register as True even if the resulting list will be empty.

I suggest instead wrapping it in a list, which fixed it for me:

if list(docinfo.traverse(nodes.author)):

To Reproduce

• Install docutils 0.18 and latest ablog
• Put metadata on a non-ABlog page
• Build the site and I think this should pop up

System Details

• docutils version: 0.18
• ablog version: latest release