Error in controller tests `undefined method '<<' for nil:NilClass`

Our test suite was failing with an error when trying to run `GaEvents::Event.new('users', 'signup')`.

I added a dummy app to the gem and a simple test case to reproduce the error, which reads as follws:

    NoMethodError:
    undefined method `<<' for nil:NilClass
    # /home/jk/gems/ga_events/lib/ga_events/list.rb:6:in `<<'

To run the test just `bundle` and run `rspec` in the gem's root directory.

It would be great if you could take a look on what is wrong there?