Crash starting nanoc 4.11.1 via Guard::Nanoc

gistfile1.txt

11:30:40 - ERROR - Guard::Nanoc failed to achieve its <start>, exception was:
> [#b39debf6872d] NoMethodError: undefined method `<<' for nil:NilClass
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/nanoc-4.11.1/lib/nanoc/cli/commands/compile_listeners/abstract.rb:54:in `on'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/nanoc-4.11.1/lib/nanoc/cli/commands/compile_listeners/file_action_printer.rb:13:in `start'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-nanoc-2.1.4/lib/guard/nanoc.rb:46:in `setup_listeners'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-nanoc-2.1.4/lib/guard/nanoc.rb:23:in `start'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/runner.rb:83:in `block (2 levels) in _supervise'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/ui/config.rb:62:in `block in with_progname'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/lumberjack-1.0.13/lib/lumberjack/logger.rb:271:in `push_thread_local_value'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/lumberjack-1.0.13/lib/lumberjack/logger.rb:232:in `set_progname'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/ui/config.rb:61:in `with_progname'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/runner.rb:81:in `block in _supervise'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/runner.rb:79:in `catch'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/runner.rb:79:in `_supervise'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/runner.rb:22:in `block (3 levels) in run'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/runner.rb:121:in `block (2 levels) in _run_group_plugins'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/runner.rb:119:in `each'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/runner.rb:119:in `block in _run_group_plugins'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/runner.rb:118:in `catch'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/runner.rb:118:in `_run_group_plugins'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/runner.rb:21:in `block (2 levels) in run'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/runner.rb:20:in `each'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/runner.rb:20:in `block in run'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/lumberjack-1.0.13/lib/lumberjack.rb:34:in `unit_of_work'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/runner.rb:18:in `run'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/commander.rb:34:in `start'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/cli/environments/valid.rb:16:in `start_guard'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/cli.rb:122:in `start'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/thor-0.20.3/lib/thor/command.rb:27:in `run'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/thor-0.20.3/lib/thor/invocation.rb:126:in `invoke_command'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/thor-0.20.3/lib/thor.rb:387:in `dispatch'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/thor-0.20.3/lib/thor/base.rb:466:in `start'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/aruba_adapter.rb:32:in `execute'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/lib/guard/aruba_adapter.rb:19:in `execute!'
> [#b39debf6872d] /Users/jmfaber/.rvm/gems/ruby-2.5.3/gems/guard-2.15.0/bin/_guard-core:11:in `<main>'