ABlog Exception Missing title from Invisible Character#

Today I got this error when building my blog based on Sphinx/ABlog extension.

sphinx.errors.ExtensionError: Handler <function process_posts> for event 'doctree-read' threw an exception (exception: Missing title)

When I remove the ABlog post directive, Sphinx indeed gives a warning about the file’s title:

WARNING: toctree contains reference to document ..... that doesn't have a title: no link will be generated [toc.no_title]

Opening the document in a Hex editor reveals that the document has a unicode character U+200B in the header marker. Removing it solved the issue.

The document was generated from PanDoc (see Merge wordpress.com site with GitHub Pages), not sure why it inserts a zero-width space.