fix: check null before typeof in isJSONSerializable

[ruguoba]

Problem

isJSONSerializable(null) throws:

Uncaught TypeError: Cannot read properties of null (reading buffer)
    at isJSONSerializable

Root Cause

typeof null returns "object", not null. So t === null (where t = typeof value) is always false — it is dead code. When value is null, it falls through to the object branch and crashes on value.buffer access.

Fix

Move the null check to use value === null before the typeof comparison:

- if (t === "string" || t === "number" || t === "boolean" || t === null) {
+ if (value === null || t === "string" || t === "number" || t === "boolean") {

Fixes #571

Summary by CodeRabbit

Bug Fixes

• Fixed JSON serialization validation to correctly recognize null values as JSON-serializable, improving data type checking accuracy across the application.

[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: 8dd34ddc-c96c-486f-aa41-39f9d9b8642e

📥 Commits

Reviewing files that changed from the base of the PR and between dfbe3ca and f9b3143.

📒 Files selected for processing (1)

• src/utils.ts

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📝 Walkthrough

Walkthrough

The isJSONSerializable utility function is corrected to properly identify null as JSON-serializable. The type-guard logic replaces a dead typeof check against null with an explicit value check, fixing a bug that caused the function to throw when passed null.

Changes

Null value JSON serialization

Layer / File(s)	Summary
Null value JSON serialization check src/utils.ts	The early-return condition in isJSONSerializable replaces t === null (unreachable since typeof never yields null) with value === null, correctly identifying null as JSON-serializable and preventing downstream null-pointer errors.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

A null that was lurking in shadows so deep,
Now sleeps as a JSON-safe value to keep,
One line, one check, the bug takes its flight—
The rabbit hops forward, the fix is just right! 🐰✨

🚥 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 specifically describes the main change: moving the null check before the typeof operation in isJSONSerializable.
Linked Issues check	✅ Passed	The PR successfully addresses issue #571 by implementing the exact fix needed: moving the null check to use value === null before typeof to properly identify null as JSON-serializable.
Out of Scope Changes check	✅ Passed	The changes are narrowly scoped to the isJSONSerializable function with only a single line change (+1/-1), directly addressing the reported bug without introducing unrelated modifications.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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