Function mutable_null_masks

cpp/src/arrow/compute/row/row_internal.h:207–210

    return data(0) + static_cast<int64_t>(row_id) * metadata_.null_masks_bytes_per_row;
  }
  uint8_t* mutable_null_masks(uint32_t row_id) {
    return mutable_data(0) +
           static_cast<int64_t>(row_id) * metadata_.null_masks_bytes_per_row;
  }
  bool is_null(uint32_t row_id, uint32_t col_pos) const {
    return bit_util::GetBit(null_masks(row_id), col_pos);
  }