public void process(Processing processing) {
        process(processing, null);
    }
Asynchronously process the given Processing using the processing
chain of this service

@throws RuntimeException caused by a QueueFullException if this DocprocService has a bounded input queue and the queue is full
@throws IllegalStateException if this DocprocService is not accepting new incoming processings
docproc/src/main/java/com/yahoo/docproc/impl/DocprocService.java