method_missing

# File railties/lib/rails/application/configuration.rb, line 604
        def method_missing(method, *args)
          if method.end_with?("=")
            @configurations[:"#{method[0..-2]}"] = args.first
          elsif args.empty?
            @configurations.fetch(method) {
              @configurations[method] = ActiveSupport::OrderedOptions.new
            }
          else
            raise ArgumentError, "wrong number of arguments (given #{args.length}, expected 0) when reading configuration `#{method}`"
          end
        end