I installed and ran railroader. It encountered an error: /var/lib/gems/2.5.0/gems/sexp_processor-4.13.0/lib/sexp.rb:222:in `line': setting s(:args).line nil (A

I installed and ran railroader. It encountered an error: /var/lib/gems/2.5.0/gems/sexp_processor-4.13.0/lib/sexp.rb:222:in `line': setting s(:args).line nil (ArgumentError) ruby 2.5.1p57