presto-main/src/main/java/io/prestosql/operator/unnest/Unnester.java/Unnester/resetInput
class Unnester:    public final void resetInput(Block block)
    {
        requireNonNull(block, "block is null");
        resetColumnarStructure(block);
        for (int i = 0; i < getChannelCount(); i++) {
            unnestBlockBuilders[i].resetInputBlock(getElementsBlock(i));
        }
        currentPosition = 0;
    }