presto-spi/src/main/java/io/prestosql/spi/block/RowBlock.java/RowBlock/fromFieldBlocks
class RowBlock:    public static Block fromFieldBlocks(int positionCount, Optional<boolean[]> rowIsNull, Block[] fieldBlocks)
    {
        int[] fieldBlockOffsets = new int[positionCount + 1];
        for (int position = 0; position < positionCount; position++) {
            fieldBlockOffsets[position + 1] = fieldBlockOffsets[position] + (rowIsNull.isPresent() && rowIsNull.get()[position] ? 0 : 1);
        }
        validateConstructorArguments(0, positionCount, rowIsNull.orElse(null), fieldBlockOffsets, fieldBlocks);
        return new RowBlock(0, positionCount, rowIsNull.orElse(null), fieldBlockOffsets, fieldBlocks);
    }