[1] How to send a custom http status code? - Kohana Forums () <http://forum.kohanaframework.org/discussion/9478/how-to-send-a-custom-http-status-code/p1>
[2] java - Is it possible to return HttpStatus status which is not from HttpStatus enum in Spring MVC - Stack Overflow () <https://stackoverflow.com/questions/42919826/is-it-possible-to-return-httpstatus-status-which-is-not-from-httpstatus-enum-in/42920039>
[3] Daniel E. Renferさんのツイート: "The HTTP status code 555 should be reserved for errors related to the server only existing in a movie or tv show." () <https://twitter.com/duck1123/status/228321909824176128>
[4] Setting the HTTP response status title, "555 - Dropbox had an error" - MuleSoft () <https://forums.mulesoft.com/questions/57701/setting-the-http-response-status-title-555-dropbox.html>