Header variables do not include the heading level

Problem

If I’m reading the documentation right (on Templates -> Section and Pages -> Table of Contents), the following Tera template code should be valid in page.html template

  {% for header in toc %}
  {{ header.level }}
  {% endfor %}

But on the terminal it instead output:

Failed to build the site
Reason: Failed to render 'page.html'
Reason: Variable `header.level` not found in context while rendering 'page.html'

Other variables like header.id and header.title works fine.
Whenever I check the context using {{ __tera_context }}, level also didn’t show up, whereas children, title, id show up.

Did I missed something in the documentation?? Or is it a bug?
I am using Zola 0.9.0

Ah the level is currently not serialized, I’m not sure why…
This will be fixed in the next release.