CORS Error on POST with no content - rest

Question

I have a controller-style REST web service endpoint which will work from the browser if I POST non-empty content, but when the content is empty, the browser returns:
No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'null' is therefore not allowed access. The response had HTTP status code 403. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.
Here is a request with content that works:
POST /my/controller/resource HTTP/1.1
Host: localhost:8083
Connection: keep-alive
Content-Length: 1
accept: application/json
Origin: null
Authorization: Bearer JWT
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.132 Safari/537.36
Content-Type: application/json
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9
HTTP/1.1 204 No Content
Server: Apache-Coyote/1.1
Access-Control-Allow-Origin: null
Access-Control-Allow-Credentials: true
Content-Language: en-US
Date: Thu, 15 Feb 2018 13:44:53 GMT
And here is a request without content that does not work
POST /my/controller/resource HTTP/1.1
Host: localhost:8083
Connection: keep-alive
Content-Length: 0
accept: application/json
Origin: null
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.132 Safari/537.36
Authorization: Bearer JWT
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9
HTTP/1.1 403 Forbidden
Server: Apache-Coyote/1.1
Content-Type: text/plain
Content-Length: 0
Date: Thu, 15 Feb 2018 13:42:16 GMT
Can anyone shed some light on why the request without content is not working - and what I might do to correct this?

Answer 1

This doesn't appear to be a CORS error - the server is set up to not allow a zero-content-length POST request. That's what's throwing the 403 error response.