'no implicit conversion of nil into String' in reader.rb

[danrue]

I'm not a big ruby guy and so I'm not sure if this is a bug, but it did take me multiple hours to figure out so I thought it is worth documenting and reporting.

While building a jekyll site, I hit the following issue:

root@6c73ddc08899:/code# bundle exec jekyll build
Configuration file: /code/_config.yml
jekyll 3.7.4 | Error:  no implicit conversion of nil into String
root@6c73ddc08899:/code# bundle exec jekyll build --trace
Configuration file: /code/_config.yml
bundler: failed to load command: jekyll (/usr/local/bundle/bin/jekyll)
TypeError: no implicit conversion of nil into String
  /usr/local/bundle/gems/jekyll-data-1.1.0/lib/jekyll-data/reader.rb:10:in `join'
  /usr/local/bundle/gems/jekyll-data-1.1.0/lib/jekyll-data/reader.rb:10:in `initialize'
  /usr/local/bundle/gems/jekyll-data-1.1.0/lib/jekyll-data.rb:50:in `new'
  /usr/local/bundle/gems/jekyll-data-1.1.0/lib/jekyll-data.rb:50:in `block in <top (required)>'
  /usr/local/bundle/gems/jekyll-3.7.4/lib/jekyll/hooks.rb:103:in `block in trigger'
  /usr/local/bundle/gems/jekyll-3.7.4/lib/jekyll/hooks.rb:102:in `each'
  /usr/local/bundle/gems/jekyll-3.7.4/lib/jekyll/hooks.rb:102:in `trigger'
  /usr/local/bundle/gems/jekyll-3.7.4/lib/jekyll/site.rb:36:in `initialize'
  /usr/local/bundle/gems/jekyll-3.7.4/lib/jekyll/commands/build.rb:30:in `new'
  /usr/local/bundle/gems/jekyll-3.7.4/lib/jekyll/commands/build.rb:30:in `process'
  /usr/local/bundle/gems/jekyll-3.7.4/lib/jekyll/commands/build.rb:18:in `block (2 levels) in init_with_program'
  /usr/local/bundle/gems/mercenary-0.3.6/lib/mercenary/command.rb:220:in `block in execute'
  /usr/local/bundle/gems/mercenary-0.3.6/lib/mercenary/command.rb:220:in `each'
  /usr/local/bundle/gems/mercenary-0.3.6/lib/mercenary/command.rb:220:in `execute'
  /usr/local/bundle/gems/mercenary-0.3.6/lib/mercenary/program.rb:42:in `go'
  /usr/local/bundle/gems/mercenary-0.3.6/lib/mercenary.rb:19:in `program'
  /usr/local/bundle/gems/jekyll-3.7.4/exe/jekyll:15:in `<top (required)>'
  /usr/local/bundle/bin/jekyll:23:in `load'
  /usr/local/bundle/bin/jekyll:23:in `<top (required)>'
root@6c73ddc08899:/code# 

My Gemfile contained:

group :jekyll_plugins do
  gem "jekyll-data"
end

With such a Gemfile, if certain themes were loaded (themes which do not use jekyll-data?), the traceback seen above is shown during 'jekyll build' or 'jekyll serve'.

Removing jekyll-data from my Gemfile solved the problem, and more than likely it never should have been there in the first place.

However, I would also expect that jekyll-data would handle such a case more gracefully.

Specifically, what it seems is happening is site.theme.data_path is set to nil, and the following line explodes

jekyll-data/lib/jekyll-data/reader.rb

Line 10 in 7aee1fb

@theme_data_files = Dir[File.join(site.theme.data_path, "**", "*.{yaml,yml,json,csv,tsv}")]

[ashmaroli]

Thank you for filing this report, @danrue.
Your deduction is spot-on. site.theme.data_path is set to nil if Jekyll doesn't find a _data directory in the theme or if it is unable to access the directory.

I didn't place a check to validate site.theme.data_path or silently convert the value to a string because I didn't expect a theme that doesn't bundle data files to load this plugin or recommend loading this plugin.

If the theme you're using doesn't have the _data directory at root and still uses this plugin, you may want to take this issue up to the theme author.

[danrue]

I understand that this situation shouldn't happen, but as a matter of fact it did for me. Note that the Gemfile that listed this plugin was in my site's folder, not a theme's folder, and so when the site changed from a theme that uses it to a theme that doesn't, it triggered this problem. But it wasn't that easy to find, because the automated build process didn't hit it for some reason.

So I guess it's up to you whether or not it's worth supporting such broken setups - at least a human readable error message would have likely saved me hours.

[ashmaroli]

Fair enough. I'll release a patch in a couple of days.
Sorry for the inconvenience caused.

[danrue]

No problem, and thank you very much. I would just like to save the next person the trouble, which may have already been accomplished by this issue report.

[alexanderadam]

I was having the same issue with the gem. But the release on GitHub is working, so I guess this fix wasn't released yet?

[ashmaroli]

Fix shipped in v1.1.1