commit: 6b2ca8a - #414 (2014-03-05 12:54:44 -0500)
links_in_common.rb:23:in `digest': can't convert nil into String (TypeError) from links_in_common.rb:23:in `<main>
Did you replace the environment variable (ENV["MOZ_SECRET_KEY"]) in line 13 with your Mozscape API secret key? Make sure both the ACCESS_ID and SECRET_KEY variables have string values.
Hope this helps.