fix: handle null and FormData order in isJSONSerializable

[leno23]

Summary

• Return true for null via explicit check (typeof null is "object")
• Check FormData / URLSearchParams before value.buffer to avoid throws on empty instances

Example

isJSONSerializable(null); // true (no throw)
isJSONSerializable(new FormData()); // false

Fixes #571
Fixes #580

Test plan

• pnpm test passes
• Added regression tests for null and FormData

Summary by CodeRabbit

• Bug Fixes

  • Enhanced JSON serialization validation to properly handle null values and correctly process form-related objects.

• Tests

  • Added comprehensive test coverage for JSON serialization detection across null, FormData, and URLSearchParams inputs.

[coderabbitai]

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 570e7f5e-a952-4d73-adef-26ea178fb42d

📥 Commits

Reviewing files that changed from the base of the PR and between 598cfa7 and 9c657a9.

📒 Files selected for processing (2)

• src/utils.ts
• test/index.test.ts

📝 Walkthrough

Walkthrough

isJSONSerializable now returns true for null via an explicit early-return and rejects FormData/URLSearchParams before accessing value.buffer. A Vitest suite was added to assert false for FormData/URLSearchParams (empty and with entries) and true for null.

Changes

Type Check Reordering and Test Coverage

Layer / File(s)	Summary
isJSONSerializable null short-circuit and instanceof reorder src/utils.ts	Adds an explicit value === null early-return and moves FormData/URLSearchParams instanceof checks before the value.buffer check.
Vitest coverage for edge cases test/index.test.ts	Adds tests that dynamically import isJSONSerializable and assert it returns false for FormData and URLSearchParams (including populated FormData) and true for null.

🎯 2 (Simple) | ⏱️ ~10 minutes

A rabbit hops through checks with care,
FormData and URLSearchParams beware!
Null is safe, buffer checks aligned,
Tests confirm the order we assigned. 🐰✨

🚥 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 summarizes the main changes: handling null correctly and reordering FormData checks before buffer property access in isJSONSerializable.
Linked Issues check	✅ Passed	The PR addresses all coding requirements from issues #571 and #580: null is now JSON-serializable, FormData/URLSearchParams checks precede buffer checks, and regression tests are added.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to fix isJSONSerializable logic and add related tests; no unrelated modifications are present.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

🧹 Nitpick comments (1)

test/index.test.ts (1)

537-544: ⚡ Quick win

Add a populated URLSearchParams assertion for symmetry.

This suite checks populated FormData but not populated URLSearchParams; adding one assertion strengthens regression coverage for the same branch behavior.

Proposed test addition

   it("returns false for FormData and URLSearchParams before buffer checks", () => {
     expect(isJSONSerializable(new FormData())).toBe(false);
     expect(isJSONSerializable(new URLSearchParams())).toBe(false);
+    expect(isJSONSerializable(new URLSearchParams({ foo: "bar" }))).toBe(false);

     const data = new FormData();
     data.append("foo", "bar");
     expect(isJSONSerializable(data)).toBe(false);
   });

🤖 Prompt for 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.

In `@test/index.test.ts` around lines 537 - 544, Add a populated URLSearchParams
assertion symmetric to the existing FormData check: in the test block that calls
isJSONSerializable for FormData and URLSearchParams, construct a URLSearchParams
instance, append a key/value (e.g., "foo", "bar"), and assert
isJSONSerializable(populatedUrlSearchParams) === false so the test covers the
populated-URLSearchParams branch alongside the populated-FormData check; locate
this in test/index.test.ts within the "returns false for FormData and
URLSearchParams before buffer checks" test that references isJSONSerializable.

🤖 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.

Nitpick comments:
In `@test/index.test.ts`:
- Around line 537-544: Add a populated URLSearchParams assertion symmetric to
the existing FormData check: in the test block that calls isJSONSerializable for
FormData and URLSearchParams, construct a URLSearchParams instance, append a
key/value (e.g., "foo", "bar"), and assert
isJSONSerializable(populatedUrlSearchParams) === false so the test covers the
populated-URLSearchParams branch alongside the populated-FormData check; locate
this in test/index.test.ts within the "returns false for FormData and
URLSearchParams before buffer checks" test that references isJSONSerializable.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 0f015ae0-802e-43fc-b28f-9808217af2bd

📥 Commits

Reviewing files that changed from the base of the PR and between dfbe3ca and 492b285.

📒 Files selected for processing (2)

• src/utils.ts
• test/index.test.ts