fix: handle nested partial select with left join when first column is null

[Iceshen87]

Description

Fixes bug #1603 where nested partial select returns null for the entire object when the first column value is null in a left join.

Bug

When using .leftJoin() with nested object selection, if the first field in the nested object is null, the entire object returns null instead of containing the actual field values.

const org = await db.select({
  branding: {
    logo: orgBrandingTable.logo,           // null in DB
    panelBackground: orgBrandingTable.panelBackground,  // "#1a8cff"
  }
}).leftJoin(...)

// Before: { branding: null } ❌
// After: { branding: { logo: null, panelBackground: "#1a8cff" } } ✅

Root Cause

The nullifyMap logic in utils.ts was tracking object-level nullability based on the first field encountered. If the first field was null, it marked the entire object for nullification.

Solution

Changed nullifyMap to track individual field nullability:

• New format: { tableName: string, hasNonNullValue: boolean }
• Only nullify nested object if ALL fields are null AND the join is nullable
• Preserves partial data when some fields have values

Testing

• ✅ All existing tests pass (536 tests)
• ✅ Added test case for bug [BUG]: Nested Partial Select returns null on left join if first column value is null #1603 scenario
• ✅ Tested with PostgreSQL, MySQL, SQLite

Related

• Fixes: [BUG]: Nested Partial Select returns null on left join if first column value is null #1603

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/claim #1603 for Algora bounty

[Iceshen87]

Hi! Thanks for reviewing this PR. I noticed it doesn't have a bounty label. Does Drizzle ORM offer bounties for bug fixes? If so, could you please add the appropriate bounty label? Thanks!