public void setHttpResponse(HttpResponse httpResponse) {
            if (httpResponse == null && this.httpResponse == null) // the handler in use returned a null response
                httpResponse = new EmptyResponse(500);
            this.httpResponse = httpResponse;
        }
This must be called before writing to this
container-core/src/main/java/com/yahoo/container/jdisc/ThreadedHttpRequestHandler.java