presto-main/src/main/java/io/prestosql/operator/unnest/ArrayOfRowsUnnester.java/ArrayOfRowsUnnester/resetColumnarStructure
class ArrayOfRowsUnnester:    @Override
    protected void resetColumnarStructure(Block block)
    {
        columnarArray = toColumnarArray(block);
        columnarRow = toColumnarRow(columnarArray.getElementsBlock());
        nullRowsEncountered = 0;
    }