public Call findCall(ComponentId processorId) {
        for (Iterator<Call> i = iterator(); i.hasNext();) {
            Call call = i.next();
            if (call.getDocumentProcessorId().equals(processorId)) {
                return call;
            }
        }
        return null;
    }
Returns the next call to this processor id, or null if no such calls are left
docproc/src/main/java/com/yahoo/docproc/CallStack.java