Issue with latest release?

Describe the bug

Automatic doc building in CI started failing right after updating myst. See the full job traceback. I copy below the piece that looks relevant to the issue at hand.

Exception occurred:
  File "/opt/hostedtoolcache/Python/3.8.7/x64/lib/python3.8/site-packages/myst_parser/docutils_renderer.py", line 79, in token_line
    raise ValueError(f"token map not set: {token}")
ValueError: token map not set: Token(type='front_matter', tag='', nesting=0, attrs=None, map=None, level=0, children=None, content={'celltoolbar': 'Raw Cell Format', 'kernelspec': {'display_name': 'Python 3', 'language': 'python', 'name': 'python3'}, 'language_info': {'codemirror_mode': {'name': 'ipython', 'version': 3}, 'file_extension': '.py', 'mimetype': 'text/x-python', 'name': 'python', 'nbconvert_exporter': 'python', 'pygments_lexer': 'ipython3', 'version': '3.8.3'}, 'toc': {'base_numbering': 1, 'nav_menu': {}, 'number_sections': True, 'sideBar': True, 'skip_h1_title': False, 'title_cell': 'Table of Contents', 'title_sidebar': 'Contents', 'toc_cell': False, 'toc_position': {}, 'toc_section_display': True, 'toc_window_display': False}}, markup='', info='', meta={}, block=False, hidden=False)
The full traceback has been saved in /tmp/sphinx-err-fd1cvqyt.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!

Environment

• Python Version [e.g. 3.7.1]: 3.8
• Operating System: ubuntu

Notes I will reproduce the issue locally as soon as I have time and try to generate a minimal example but I figured it may be worth it to post it and see if it has happened to other people.

[chrisjsewell]

myst-parser==0.13.3 and myst-nb==0.11.1

[OriolAbril]

Cool, thanks @chrisjsewell, looks like it’s not necessary to generate a minimal example. Thanks for the super quick fix.