Fix handling of "undefined"

[kibertoad]

Summary by CodeRabbit

• Documentation

  • Clarified null vs undefined semantics and cache layer configuration guidance.

• Bug Fixes

  • Cache now treats null as a resolved empty value (cached) and undefined as unresolved (not cached, continues querying).

• Tests

  • Added tests validating that null updates cache and undefined does not; adjusted expectations accordingly.

• Chores

  • Dependency bumps for runtime and dev tooling.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

Walkthrough

This PR separates null and undefined semantics: null is a resolved-but-empty value that is cached and stops further sources; undefined means unresolved, is not cached, and allows subsequent data sources to be queried. Tests, docs, and loader logic updated to reflect this.

Changes

Cohort / File(s)	Summary
Documentation Updates README.md	Clarified semantics: null = resolved-empty (cached, stops querying), undefined = unresolved (not cached, continue to next source). Added note that memory/async cache layers are optional and skipped if unconfigured.
Core Loader Logic lib/Loader.ts, lib/GroupLoader.ts	Simplified per-source handling: only defined (non-undefined) results are cached and returned as-is (including null); undefined continues to next data source; after all sources, throw if throwIfUnresolved else return undefined. Removed final mapping of undefined→null.
Type Documentation lib/types/DataSources.ts	Added JSDoc for DataSource and GroupDataSource describing return semantics and caching implications for null vs undefined (no signature changes).
Tests test/Loader-main.spec.ts, test/GroupLoader-main.spec.ts	Added tests asserting: no cache update when all sources return undefined; cache set when a source returns explicit null; updated expectations where prior behavior returned null to now return undefined when unresolved.
Metadata / Tooling package.json	Bumped dependency/devDependency versions: ioredis → ^5.8.2, vitest → ^3.2.4, typescript → ^5.9.3.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

• Inspect loadFromLoaders paths in both lib/Loader.ts and lib/GroupLoader.ts to confirm only defined values are cached and returned.
• Verify throw semantics after exhausting sources (respecting throwIfUnresolved).
• Confirm tests in test/* reflect new expectations for undefined vs null.
• Quick skim of README and JSDoc for accurate, consistent wording.

Poem

A rabbit peeks where loaders run,
Null hums "I'm found" beneath the sun,
Undefined skips on, nose to the breeze,
Caches stay tidy, queries find ease —
Hoppity-hop, the data's fun! 🐇

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Fix handling of "undefined"' directly addresses the core change: distinguishing between null (resolved-but-empty, cached) and undefined (unresolved, not cached) throughout the codebase.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/null-vs-undefined

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📜 Recent review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between c596fd4 and 7356c40.

📒 Files selected for processing (3)

• lib/GroupLoader.ts (2 hunks)
• lib/Loader.ts (2 hunks)
• package.json (2 hunks)

🚧 Files skipped from review as they are similar to previous changes (2)

• lib/GroupLoader.ts
• lib/Loader.ts

🔇 Additional comments (1)

package.json (1)

53-53: No action needed for dependency version compatibility.

The dependency updates are conservative within their caret ranges (ioredis ^5.6.1→^5.8.2, vitest ^3.2.0→^3.2.4, typescript ^5.8.3→^5.9.3). Code inspection shows only standard, stable ioredis APIs in use (constructor, defineCommand, flushall, disconnect) with no deprecated patterns. These are routine maintenance updates with no impact on the null/undefined fix logic in the loader.

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