presto-main/src/main/java/io/prestosql/operator/unnest/Unnester.java/Unnester/buildOutputBlocksAndFlush
class Unnester:    public final Block[] buildOutputBlocksAndFlush()
    {
        Block[] outputBlocks = new Block[getChannelCount()];
        for (int i = 0; i < getChannelCount(); i++) {
            outputBlocks[i] = unnestBlockBuilders[i].buildOutputAndFlush();
        }
        return outputBlocks;
    }