Crash if collection is empty

[sim642]

Originally posted at alshedivat/al-folio#2866 (comment):

Since https://github.com/george-gca/jekyll-archives-v2 doesn't allow issues for some reason, I don't have anywhere else to report this but here.
For me, it crashes with

/var/lib/gems/3.2.0/gems/jekyll-archives-v2-0.0.6/lib/jekyll-archives-v2.rb:111:in `years': undefined method `docs' for nil:NilClass (NoMethodError)

        date_attr_hash(documents.docs, "%Y")
                                ^^^^^
        from /var/lib/gems/3.2.0/gems/jekyll-archives-v2-0.0.6/lib/jekyll-archives-v2.rb:93:in `read_dates'
        from /var/lib/gems/3.2.0/gems/jekyll-archives-v2-0.0.6/lib/jekyll-archives-v2.rb:62:in `read'
        from /var/lib/gems/3.2.0/gems/jekyll-archives-v2-0.0.6/lib/jekyll-archives-v2.rb:51:in `block in generate'
        from /var/lib/gems/3.2.0/gems/jekyll-archives-v2-0.0.6/lib/jekyll-archives-v2.rb:50:in `each'
        from /var/lib/gems/3.2.0/gems/jekyll-archives-v2-0.0.6/lib/jekyll-archives-v2.rb:50:in `generate'
        from /var/lib/gems/3.2.0/gems/jekyll-4.3.4/lib/jekyll/site.rb:193:in `block in generate'
        from /var/lib/gems/3.2.0/gems/jekyll-4.3.4/lib/jekyll/site.rb:191:in `each'
        from /var/lib/gems/3.2.0/gems/jekyll-4.3.4/lib/jekyll/site.rb:191:in `generate'
        from /var/lib/gems/3.2.0/gems/jekyll-4.3.4/lib/jekyll/site.rb:79:in `process'
        from /var/lib/gems/3.2.0/gems/jekyll-4.3.4/lib/jekyll/command.rb:28:in `process_site'
        from /var/lib/gems/3.2.0/gems/jekyll-4.3.4/lib/jekyll/commands/build.rb:65:in `build'
        from /var/lib/gems/3.2.0/gems/jekyll-4.3.4/lib/jekyll/commands/build.rb:36:in `process'
        from /var/lib/gems/3.2.0/gems/jekyll-4.3.4/lib/jekyll/command.rb:91:in `block in process_with_graceful_fail'
        from /var/lib/gems/3.2.0/gems/jekyll-4.3.4/lib/jekyll/command.rb:91:in `each'
        from /var/lib/gems/3.2.0/gems/jekyll-4.3.4/lib/jekyll/command.rb:91:in `process_with_graceful_fail'
        from /var/lib/gems/3.2.0/gems/jekyll-4.3.4/lib/jekyll/commands/build.rb:18:in `block (2 levels) in init_with_program'
        from /var/lib/gems/3.2.0/gems/mercenary-0.4.0/lib/mercenary/command.rb:221:in `block in execute'
        from /var/lib/gems/3.2.0/gems/mercenary-0.4.0/lib/mercenary/command.rb:221:in `each'
        from /var/lib/gems/3.2.0/gems/mercenary-0.4.0/lib/mercenary/command.rb:221:in `execute'
        from /var/lib/gems/3.2.0/gems/mercenary-0.4.0/lib/mercenary/program.rb:44:in `go'
        from /var/lib/gems/3.2.0/gems/mercenary-0.4.0/lib/mercenary.rb:21:in `program'
        from /var/lib/gems/3.2.0/gems/jekyll-4.3.4/exe/jekyll:15:in `<top (required)>'
        from /usr/local/bin/jekyll:25:in `load'
        from /usr/local/bin/jekyll:25:in `<main>'

Also I'm very confused about that repository because it only has 0.0.5 (

jekyll-archives-v2/lib/jekyll-archives-v2/version.rb

Line 5 in 35e540e

VERSION = "0.0.5"

), so where is this 0.0.6 coming from?

I since realized what causes it: if a collection exists and has output: true, but has no documents, then this crash occurs.
The workaround is to just also disable the collection output for now.

What I imagine should happen is that maybe there's a warning in the build output, but not crash.