def render_404_public_file!(file_name)
      four_oh_four_path = File.expand_path("#{file_name}.html", settings.public_dir)
      return unless File.file?(four_oh_four_path)
      send_file four_oh_four_path, status: 404
    end
def render_404_public_file!(file_name)
      four_oh_four_path = File.expand_path("#{file_name}.html", settings.public_dir)
      return unless File.file?(four_oh_four_path)
      send_file four_oh_four_path, status: 404
    end
Given a file name, attempts to send an public 404 file, if it exists, and halt

 @param [String] file_name