presto-main/src/main/java/io/prestosql/operator/unnest/UnnestBlockBuilder.java/UnnestBlockBuilder/resetInputBlock
class UnnestBlockBuilder:    public void resetInputBlock(Block block)
    {
        this.source = requireNonNull(block, "block is null");
        // output and null-check have to be cleared because the source has changed
        clearCurrentOutput();
        nullFinder.resetCheck();
    }