The Problem is this section in v0.12.0 (the one you are using) https://github.com/drapergem/draper/blob/v0.12.0/lib/draper/railtie.rb#L5-L8
When I look at the master branch they changed to code to look like: https://github.com/drapergem/draper/blob/master/lib/draper/railtie.rb#L5-L10
You should upgrade your draper gem to the latest release and see if the error still occurs.