NoMethodError: undefined `[] 'method for nil: NilClass when clicking on Heroku

Question

Rails noob is here.

I ran into a problem when clicking on Heroku (NoMethodError: undefined `[] 'method for nil: NilClass). I'm not even sure where I should start looking for this problem.

remote: -----> Preparing app for Rails asset pipeline
remote:        Running: rake assets:precompile
remote:        I, [2015-10-04T23:27:47.570225 #397]  INFO -- : Writing /tmp/build_1a2df3ea1a8121d7fba6ab542c59ba85/public/assets/application-7fbbda11565ec9a0d53aaeb338357988655d4d81476f99312f8a66772c63bea9.js
remote:        rake aborted!
remote:        NoMethodError: undefined method `[]' for nil:NilClass
remote:        /tmp/build_1a2df3ea1a8121d7fba6ab542c59ba85/vendor/bundle/ruby/2.2.0/gems/sprockets-3.3.5/lib/sprockets/sass_processor.rb:266:in `sprockets_context'
remote:        

Answer 1

I managed to solve this problem by renaming the application.css file to application.css.scss.