nanoc issue repro

bundle exec nanoc check stale fails when removing useless :excerpt representation of pictures (output/photos/The_Osborne_Apartments-excerpt.jpeg). Everything works as expected in terms of routing and compilation, only check fails.

Steps to reproduce

$ bundle install
$ rm -rf output && bundle exec nanoc && bundle exec nanoc check stale

Output:

$ rm -rf output && bundle exec nanoc && bundle exec nanoc check stale
Loading site… done
Compiling site…
      create  [0.00s]  output/photos/The_Osborne_Apartments-default.jpeg
      create  [0.00s]  output/photos/WoodStorkWhole-default.jpeg
      create  [0.00s]  output/photos/WoodStorkWhole-excerpt.jpeg
      create  [0.00s]  output/index.html
      create  [0.01s]  output/2020/12/23/test/index.html

Site compiled in 0.23s.
Loading site… done
  Running check stale…   error
Issues found!
  output/photos/WoodStorkWhole-excerpt.jpeg:
    [ ERROR ] stale - file without matching item

Error: One or more checks failed

Commenting code related to all_excerpt_pictures in preprocess L11-16 and route L66 fixes the issue (but routes pictures not needed (output/photos/The_Osborne_Apartments-excerpt.jpeg)).

Output:

$ rm -rf output && bundle exec nanoc && bundle exec nanoc check stale
Loading site… done
Compiling site…
      create  [0.00s]  output/photos/The_Osborne_Apartments-excerpt.jpeg
      create  [0.00s]  output/photos/The_Osborne_Apartments-default.jpeg
      create  [0.00s]  output/photos/WoodStorkWhole-excerpt.jpeg
      create  [0.00s]  output/photos/WoodStorkWhole-default.jpeg
      create  [0.00s]  output/index.html
      create  [0.03s]  output/2020/12/23/test/index.html

Site compiled in 0.21s.
Loading site… done
  Running check stale…   ok