Add Explicit \N NULL Marker for CSV Export/Import of TEXT Fields

[inv-jishnu]

Description

This PR introduces consistent handling of NULL values for TEXT fields when exporting and importing CSV files.
When exporting data to CSV, TEXT columns with null values are now written as \N.
During CSV import, any \N value is interpreted as a real null.

This ensures reliable round-trip data integrity for TEXT fields, addressing issues where "null" string values and actual null values were previously indistinguishable in CSV exports.

This change was introduced based on discussion from https://scalar-labs.slack.com/archives/C043ATSHAQL/p1763548538773339?thread_ts=1763536825.886369&cid=C043ATSHAQL.

Related issues and/or PRs

NA

Changes made

• CSV Export
  If a TEXT field value is null, the exported CSV now adds \N instead of null.

• CSV Import
  When reading CSV files, the value \N for text field it is interpreted as a real null.

Checklist

The following is a best-effort checklist. If any items in this checklist are not applicable to this PR or are dependent on other, unmerged PRs, please still mark the checkboxes after you have read and understood each item.

• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation to reflect the changes.
• I have considered whether similar issues could occur in other products, components, or modules if this PR is for bug fixes.
• Any remaining open issues linked to this PR are documented and up-to-date (Jira, GitHub, etc.).
• Tests (unit, integration, etc.) have been added for the changes.
• My changes generate no new warnings.
• Any dependent changes in other PRs have been merged and published.

Additional notes (optional)

NA

Release notes

Add Explicit \N NULL Marker for CSV Export/Import of TEXT Fields

[gemini-code-assist]

Summary of Changes

Hello @inv-jishnu, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a standardized mechanism for handling null values in TEXT fields during CSV export and import operations. By implementing "\N" as an explicit marker for nulls in TEXT columns, the changes eliminate data integrity issues where actual nulls could be confused with the string literal "null", thereby ensuring accurate round-trip data processing.

Highlights

• CSV Export Enhancement: TEXT columns with null values are now explicitly written as "\N" in CSV exports, ensuring a clear distinction from the string literal "null".
• CSV Import Interpretation: During CSV import, the "\N" string found in TEXT fields is now correctly interpreted as a real null value, completing the round-trip consistency.
• Improved Data Integrity: This change ensures reliable round-trip data integrity for TEXT fields, resolving previous ambiguity where actual null values and the string "null" were indistinguishable.

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[gemini-code-assist]

Code Review

This pull request introduces a consistent way to handle NULL values for TEXT fields during CSV export and import, which is a great improvement for data integrity.

My main feedback is regarding the choice of the NULL marker. The implementation uses the literal string "/N", whereas the pull request description and common conventions (like MySQL's) use \N. Using \N is the standard way to represent NULL in many bulk data formats.

I've left specific comments with suggestions to change "/N" to "\\N" in the code and update the corresponding tests. I've also suggested a small refactoring to improve code readability in ColumnUtils.java.

Addressing these points will make the feature more robust and aligned with industry standards.

[ypeckstadt]

LGTM. Thank you.

[Torch3333]

LGTM, thank you!

[thongdk8]

LGTM! Thank you!

[feeblefakie]

LGTM! Thank you!

[komamitsu]

LGTM! 👍

[brfrn169]

LGTM! Thank you