config/routes.rb in rails-sandbox-assets-0.2.0 vs config/routes.rb in rails-sandbox-assets-0.2.1

@@ -1,6 +1,8 @@
 SandboxAssets::Engine.routes.draw do
-  mount Rails.application.assets => Rails.configuration.assets.prefix
+  # When the application is booted by sidekiq (tested with 4.0.1) Rails.application.assets may not
+  # be loaded
+  mount Rails.application.assets => Rails.configuration.assets.prefix if Rails.application.assets
   get '_iframe/*path' => 'sandbox_assets/test_runner#iframe', format: false,
     as: :sandbox_assets_iframe
   ['', '*path'].each do |p|
     get p => 'sandbox_assets/test_runner#index', format: false
   end