public Response process(Request request) {
        Processor processor = next();
        if (processor == null)
            return defaultResponse(request);

        Response response = null;
        try {
            nextProcessor();
            onInvoking(request, processor);
            response = processor.process(request, this);
            if (response == null)
                throw new NullPointerException(processor + " returned null, not a Response object");
            return response;
        } finally {
            previousProcessor();
            onReturning(request, processor, response);
        }
    }
Calls process on the next processor in this chain. If there is no next, an empty response is returned.
container-core/src/main/java/com/yahoo/processing/execution/Execution.java