presto-main/src/main/java/io/prestosql/operator/JoinProbe.java/JoinProbe/currentRowContainsNull
class JoinProbe:    private boolean currentRowContainsNull()
    {
        for (Block probeBlock : probeBlocks) {
            if (probeBlock.isNull(position)) {
                return true;
            }
        }
        return false;
    }