No Content - RFC 7231
204 No Content indicates that the server has successfully fulfilled the request and that there is no additional content to send in the response payload body. Metadata in the response header fields refer to the target resource and its selected representation after the requested action was applied.
For example, if a 204 status code is received in response to a
PUT request and the response contains an ETag header field, then the
PUT was successful and the ETag field-value contains the entity-tag for the new representation of that target resource.
A 204 response is terminated by the first empty line after the header fields because it cannot contain a message body and is cacheable by default.