Upgrade to Rails 6.0 and apply new framework defaults

config/initializers/action_mailer.rb

@@ -1,3 +1,7 @@
+# frozen_string_literal: true
+
+require 'code_ocean/config'
+
 CodeOcean::Config.new(:action_mailer).read.each do |key, value|
   CodeOcean::Application.config.action_mailer.send(:"#{key}=", value.respond_to?(:symbolize_keys) ? value.symbolize_keys : value)
 end