Error when handling empty "Access-Control-Request-Headers" header

$ curl 'http://localhost:15984/_session' -H "Access-Control-Request-Headers:" -H "Access-Control-Request-Method: POST" -H "Origin:https://something.com" -XOPTIONS -v
Mon  1 Aug 2016 13:48:26 BST
*   Trying ::1...
* connect to ::1 port 15984 failed: Connection refused
*   Trying 127.0.0.1...
* Connected to localhost (127.0.0.1) port 15984 (#0)
> OPTIONS /_session HTTP/1.1
> Host: localhost:15984
> User-Agent: curl/7.43.0
> Accept: */*
> Access-Control-Request-Method: POST
> Origin:https://something.com
> 
< HTTP/1.1 204 No Content
< Access-Control-Allow-Credentials: true
< Access-Control-Allow-Headers: 
< Access-Control-Allow-Methods: GET, PUT, POST, HEAD, DELETE
< Access-Control-Allow-Origin: https://something.com
< Access-Control-Max-Age: 600
< Content-Length: 0
< Date: Mon, 01 Aug 2016 12:48:25 GMT
< Server: CouchDB/b49d069 (Erlang OTP/18)
< X-Couch-Request-ID: c68c601375
< X-CouchDB-Body-Time: 0
< 
* Connection #0 to host localhost left intact

$ curl 'http://localhost:15984/_session' -H "Access-Control-Request-Headers;" -H "Access-Control-Request-Method: POST" -H "Origin:https://something.com" -XOPTIONS -v
Mon  1 Aug 2016 13:48:21 BST
*   Trying ::1...
* connect to ::1 port 15984 failed: Connection refused
*   Trying fe80::1...
* connect to fe80::1 port 15984 failed: Connection refused
*   Trying 127.0.0.1...
* Connected to localhost (127.0.0.1) port 15984 (#0)
> OPTIONS /_session HTTP/1.1
> Host: localhost:15984
> User-Agent: curl/7.43.0
> Accept: */*
> Access-Control-Request-Headers:
> Access-Control-Request-Method: POST
> Origin:https://something.com
> 
< HTTP/1.1 405 Method Not Allowed
< Access-Control-Allow-Credentials: true
< Access-Control-Allow-Origin: https://something.com
< Access-Control-Expose-Headers: content-type, cache-control, accept-ranges, etag, server, x-couch-request-id, x-couch-update-newrev, x-couchdb-body-time
< Allow: GET,HEAD,POST,DELETE
< Cache-Control: must-revalidate
< Content-Length: 76
< Content-Type: application/json
< Date: Mon, 01 Aug 2016 12:48:21 GMT
< Server: CouchDB/b49d069 (Erlang OTP/18)
< 
{"error":"method_not_allowed","reason":"Only GET,HEAD,POST,DELETE allowed"}
* Connection #0 to host localhost left intact