fix: nullable not respected for objects with nullable properties #533

[bankyadam]

Summary

Fixes #533 - Resolves incorrect null handling for nullable parent objects containing nullable child properties.

Problem

When a schema defined a nullable object (type: object, nullable: true) with child properties that were also nullable, the generator was incorrectly adding an additional | null to the parent type. This happened because isNullMissingInType was detecting the | null from nested properties and incorrectly concluding that the parent type needed null added.

Example Issue

Given this schema:

{
  "type": "object",
  "nullable": true,
  "properties": {
    "email": { "type": "string", "nullable": true }
  }
}

Before: Generated redundant | null even though the parent was already properly nullable After: Correctly generates { email?: string | null } | null

Solution

Refactored the isNullMissingInType method in src/schema-parser/schema-utils.ts to distinguish between:

• Root-level nullable types (union with null at the top level)
• Types with nested nullable properties (objects containing prop: string | null)

The fix uses regex patterns to detect only root-level null unions:

• Pattern ending with | null
• Pattern starting with null |
• Exact match of null

This prevents false positives from nested nullable properties while correctly identifying when the parent type actually needs | null added.

Changes

Core Fix

• src/schema-parser/schema-utils.ts: Improved isNullMissingInType logic with regex-based root-level null detection

Build Configuration

• package.json: Changed ESM output extensions from .js to .mjs for better module resolution

Test Coverage

• Added new test suite: tests/spec/nullable-parent-with-nullable-children/
• Tests cover nullable parent objects with nullable child properties, nested nullable objects, and complex scenarios
• Updated snapshots across multiple test suites to reflect correct nullable handling

Testing

All existing tests pass with updated snapshots showing correct nullable type generation. New test suite specifically validates the fix for nested nullable scenarios.

---

[!NOTE] Fixes null handling by only adding | null at the root type level, adds targeted tests, and updates snapshots accordingly.

• Core Fix
  • Refactor src/schema-parser/schema-utils.ts:isNullMissingInType to detect only root-level null in unions (regex-based), avoiding false positives from nested nullable properties.
  • safeAddNullToType now leverages the corrected check to prevent duplicate | null on parent object types.
• Tests
  • Add tests/spec/nullable-parent-with-nullable-children/ suite with schema and snapshot validating nullable parent + nullable children behavior.
  • Update snapshots (tests/__snapshots__/extended.test.ts.snap, tests/__snapshots__/simple.test.ts.snap, tests/spec/additional-properties-2.0/__snapshots__/basic.test.ts.snap) to reflect corrected nullability (e.g., unions with null, nullable record values).
• Meta
  • Add changeset .changeset/giant-hats-work.md (patch).

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