fix: handle null in isJSONSerializable to prevent TypeError

[Zelys-DFKH]

Fixes #571 — isJSONSerializable crashes with TypeError when passed null.

Root cause:

• Line 22 checks t === null instead of value === null
• Since typeof null === "object" (JavaScript quirk), this condition never matches (dead code)
• Execution reaches line 28: if (value.buffer) → crashes on null

Solution:

• Add explicit null check in early return alongside undefined
• Remove unreachable t === null condition (typeof always returns a string, never "null")

Changes:

• src/utils.ts: 2-line fix (add null guard, remove dead condition)
• test/index.test.ts: 6 regression tests covering null, undefined, primitives, objects, special cases

Test results: 34/34 passing ✅

• All 28 existing tests pass
• All 6 new regression tests pass (including null crash case)

Summary by CodeRabbit

• Bug Fixes

  • Treat null and undefined as non-serializable in validation, preventing them from being accepted as valid serialized values.

• Tests

  • Added comprehensive test coverage for serialization validation across primitives, plain objects/arrays, typed arrays, binary buffers, and form-encoded data.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: f506ee81-da28-47e0-82f5-a2804a274998

📥 Commits

Reviewing files that changed from the base of the PR and between 93f1cde and 852f41f.

📒 Files selected for processing (1)

• test/index.test.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• test/index.test.ts

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📝 Walkthrough

Walkthrough

The PR makes isJSONSerializable return false for both undefined and null and adds a Vitest suite verifying behavior for null, undefined, primitives, plain objects/arrays, Uint8Array/ArrayBuffer, FormData, and URLSearchParams.

Changes

isJSONSerializable Bug Fix

Layer / File(s)	Summary
Core Logic Fix src/utils.ts	Function now returns false for both undefined and null in the initial guard clause, preventing null dereference in later type checks.
Test Coverage test/index.test.ts	New isJSONSerializable test suite verifies expected return values for null, undefined, primitives, plain objects/arrays, Uint8Array/ArrayBuffer, FormData, and URLSearchParams.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

A rabbit nudged a null aside,
"No crash today," it sweetly cried.
With tests in place and guards that sing,
Our JSON checker hops on spring.
✨🐰

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main fix: handling null in isJSONSerializable to prevent TypeError, which matches the primary change in the changeset.
Linked Issues check	✅ Passed	The PR fully addresses all coding requirements from issue #571: fixes the incorrect null check, ensures null is treated as JSON-serializable, prevents property access on null, and adds comprehensive regression tests.
Out of Scope Changes check	✅ Passed	All changes are directly related to fixing the null handling bug in isJSONSerializable; no unrelated modifications are present in the changeset.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@test/index.test.ts`:
- Around line 558-561: The test description is misleading because ArrayBuffer
doesn't have a .buffer property and so the isJSONSerializable branch checking
value.buffer isn't exercised; update the test(s) so one explicitly uses a
TypedArray (e.g., new Uint8Array(10)) to hit the value.buffer branch and assert
isJSONSerializable(...) === false, and either rename the existing ArrayBuffer
test to reflect "returns false for ArrayBuffer" or split into two tests: one for
TypedArray (exercises value.buffer) and one for ArrayBuffer (verifies
non-serializable via constructor check) while keeping references to the
isJSONSerializable function in the test names for clarity.
- Line 538: Add the same ESLint suppression used elsewhere for null to the
failing assertion: before the expect(isJSONSerializable(null)) call add an
inline comment to disable the unicorn/no-null rule for the next line so CI won't
fail; locate the expect call referencing isJSONSerializable and add the same "//
eslint-disable-next-line unicorn/no-null" style suppression used at lines 58 and
208.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 6e89410c-737a-4086-b1cf-7a91ad5029ca

📥 Commits

Reviewing files that changed from the base of the PR and between dfbe3ca and 93f1cde.

📒 Files selected for processing (2)

• src/utils.ts
• test/index.test.ts