fix: correct isJSONSerializable to handle null without throwing

[EduardF1]

Problem

isJSONSerializable(null) throws a TypeError and incorrectly returns
alse.

Root cause

// src/utils.ts
const t = typeof value;
if (t === "string" || t === "number" || t === "boolean" || t === null) {
  return true;
}
// ...
if (value.buffer) { // <-- throws TypeError when value is null

Two bugs on the same line:

1. Dead code: ypeof value never returns "null" — it returns "object" for
   ull. So === null can never be rue.
2. Throws on null: Since the early-return check is never triggered for
   ull, execution continues to
   alue.buffer, which throws TypeError: Cannot read properties of null (reading 'buffer').

Verified:
ull is valid JSON (JSON.stringify(null) → "null"), so the function should return rue for it.

Fix

Replace === null with
alue === null:

// Before
if (t === "string" || t === "number" || t === "boolean" || t === null) {

// After
if (t === "string" || t === "number" || t === "boolean" || value === null) {

This correctly checks the value itself rather than its ypeof result, so
ull hits the early
eturn true before reaching
alue.buffer.

Fixes #571

Summary by CodeRabbit

• Bug Fixes
  • Fixed JSON serializability checks so null is now correctly treated as a valid JSON value.
• Tests
  • Added coverage to confirm null returns true in the JSON serializability check.

[magion33]

@EduardF1 I'm the creator of the issue and this is exactly what fix I had in mind. LGTM

Note: Another partially related thing is that the body serialization logic of the fetch here

    if (context.options.body && isPayloadMethod(context.options.method)) {
      if (isJSONSerializable(context.options.body)) {
         ...

doesn't allow to have a body of "" (empty string), or 0, or null. All of those are technically valid JSON-serializable values and should be allowed imo.

[EduardF1]

@magion33 thanks for the LGTM, and good catch on the body-serialization gap. Looking at https://github.com/unjs/ofetch/blob/main/src/fetch.ts#L130:

if (context.options.body && isPayloadMethod(context.options.method)) {

The leading context.options.body && is the part that drops "", 0, and null before isJSONSerializable is even consulted. Replacing it with an explicit `!== undefined` check (and handling those primitives in the stringify branch) is the right fix, but it's a separate concern from #571 — different file, different surface area, different test coverage.

I'd prefer to keep this PR narrowly focused on the dead-code/throws-on-null bug so it's easy for maintainers to review and merge, and then land the body-serialization fix as a follow-up that references this one. Happy to open that follow-up PR right after this merges (or in parallel if a maintainer signals it's fine to bundle).

[magion33]

@EduardF1 Yes, I agree. It's a different topic, just slightly related.

[EduardF1]

Summary

Fixes isJSONSerializable(null) throwing instead of returning false, preventing unintended errors when null is passed as a request body (fixes #571).

Status

• CI: ✅ All checks passing
• Issue reporter (@magion33) confirmed this matches their intent
• Two-line fix in utils.ts with test coverage for the null path
• Ready for review

@pi0 happy to adjust scope or naming if needed. Thanks!

[EduardF1]

Thanks again @magion33 for validating the fix and for agreeing to keep the body-serialization case separate. I am happy to send that follow-up on its own after this one lands if maintainers want it.

[EduardF1]

Hi team, checking in on this PR! Let me know if you have any questions.

[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: 9a6746c6-9dd8-47ae-8d82-5449c80f16d9

📥 Commits

Reviewing files that changed from the base of the PR and between dfbe3ca and a6cf69a.

📒 Files selected for processing (2)

• src/utils.ts
• test/index.test.ts

---

📝 Walkthrough

Walkthrough

Fixes a bug in isJSONSerializable where typeof value === null (always false) was used instead of value === null, causing null to not be recognized as JSON-serializable and throwing a TypeError. Adds a test asserting isJSONSerializable(null) returns true.

null serialization fix

Layer / File(s)	Summary
Fix null check and add test coverage src/utils.ts, test/index.test.ts	Replaces typeof value === null with value === null in isJSONSerializable; imports the function in the test suite and adds a case asserting isJSONSerializable(null) returns true.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

🐇 A null walked in, was turned away,
typeof lied and caused dismay.
Now === null sets things right,
serializable null, shining bright!
No more TypeError in the night~ 🌙

🚥 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 without throwing.
Linked Issues check	✅ Passed	The changes directly address #571 by making null JSON-serializable and adding a test for the null case.
Out of Scope Changes check	✅ Passed	The PR stays narrowly scoped to the null-handling bug and its test coverage, with no unrelated changes.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.55%. Comparing base (27996d3) to head (a6cf69a).
⚠️ Report is 103 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #572       +/-   ##
===========================================
+ Coverage   56.86%   85.55%   +28.68%     
===========================================
  Files          16        5       -11     
  Lines         728      263      -465     
  Branches      113      133       +20     
===========================================
- Hits          414      225      -189     
+ Misses        303       33      -270     
+ Partials       11        5        -6     

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