# File lib/faraday.rb, line 160
    def register_middleware(autoload_path = nil, mapping = nil)
      if mapping.nil?
        mapping = autoload_path
        autoload_path = nil
      end
      middleware_mutex do
        @middleware_autoload_path = autoload_path if autoload_path
        (@registered_middleware ||= {}).update(mapping)
      end
    end