Unable to preview the docs locally

I've followed the steps in order to have it working but I'm seeing this error when trying to launch the server:

[ruben@mbp ~/projects/gitlab-docs (master)]$ bundle exec nanoc
Loading site… done
Compiling site…

Captain! We’ve been hit!

NoMethodError: undefined method `path' for nil:NilClass

Current item: /ee/tools/email.md (:default representation)

  0. layout /header.html:13:in `block in get_binding'
  1. layout /header.html:10:in `each'
  2. layout /header.html:10:in `get_binding'
  3. /Users/ruben/.rbenv/versions/2.4.0/lib/ruby/2.4.0/erb.rb:896:in `eval'
  4. /Users/ruben/.rbenv/versions/2.4.0/lib/ruby/2.4.0/erb.rb:896:in `result'
  5. /Users/ruben/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/nanoc-4.8.19/lib/nanoc/filters/erb.rb:36:in `run'
  6. /Users/ruben/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/nanoc-4.8.19/lib/nanoc/base/services/filter.rb:152:in `setup_and_run'
  7. /Users/ruben/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/nanoc-4.8.19/lib/nanoc/helpers/rendering.rb:54:in `render'
  8. layout /default.html:5:in `get_binding'
  9. /Users/ruben/.rbenv/versions/2.4.0/lib/ruby/2.4.0/erb.rb:896:in `eval'
  ... 16 lines omitted (see crash.log for details)

A detailed crash log has been written to ./crash.log.

/cc @axil @marcia