@Override
    public VisitorResponse getNext(int timeoutMilliseconds) throws InterruptedException {
        if (params.getLocalDataHandler() == null) {
            throw new IllegalStateException("Data has been routed to external source for this visitor");
        }
        return params.getLocalDataHandler().getNext(timeoutMilliseconds);
    }
Schedule a new SendCreateVisitors task iff there are still buckets to
visit, the visiting has not failed fatally and we haven't already
scheduled such a task. Return whether a visitor was scheduled here.
documentapi/src/main/java/com/yahoo/documentapi/messagebus/MessageBusVisitorSession.java