presto-main/src/main/java/io/prestosql/operator/JoinProbe.java/JoinProbe/getCurrentJoinPosition
class JoinProbe:    public long getCurrentJoinPosition(LookupSource lookupSource)
    {
        if (currentRowContainsNull()) {
            return -1;
        }
        if (probeHashBlock.isPresent()) {
            long rawHash = BIGINT.getLong(probeHashBlock.get(), position);
            return lookupSource.getJoinPosition(position, probePage, page, rawHash);
        }
        return lookupSource.getJoinPosition(position, probePage, page);
    }