Incorrect parsing of 204 response

[jely2002]

If a deletion request is successful, the server MUST return either a 200 OK status code and response document (as described above) or a 204 No Content status code with no response document.

https://jsonapi.org/format/#crud-deleting-responses

As can be seen in the JSON:API spec a server can also return a 204 with empty content. Right now this blows up, as the delete method on the document client will try to parse the response. Which will fail as we then try to json_decode an empty string, which is not valid JSON.

I propose to handle the 204 in the response parser and return an empty document to fix this problem.

[jely2002]

Seems the bug here is that a request can have an unknown size in this case the size will be -1 or 0. To fix this I'll have to peek at the content to check if there is any.