Problem
You are using the tr8n translation engine, which works fine in your local development environment, and you want to use it in an environment called ‘staging’, but after deployment you get the following error in your log files;

NoMethodError (undefined method `[]' for nil:NilClass):                                                                                                                                                                                       
  will_filter (3.1.9) lib/will_filter/config.rb:92:in `user_filters_enabled?'                                                                                                                                                                 
  will_filter (3.1.9) lib/will_filter/extensions/action_controller_extension.rb:34:in `init_will_filter'

Solution

The default configuration file for will_filter includes an environment called ‘stage’ and not ‘staging’.
So you can add the following into the config/will_filter/config.yml file in your application (just afer the stage: line):

staging:
  <<: *defaults