void skipCurrentBucket() {
        if (buckets.containsKey(bucketToKeyWrapper(getCurrentBucketId())))
            throw new IllegalStateException("Current bucket was already added to the explicit bucket set");

        ++finishedBucketCount;
        ++bucketCursor;
    }
Marks the current bucket as finished and advances the bucket cursor;
throws instead if the current bucket is already {@link #addBucket added}.
documentapi/src/main/java/com/yahoo/documentapi/ProgressToken.java