From f593d42e5b47723cdf13a9b441b040d2166898f6 Mon Sep 17 00:00:00 2001
From: Rafael Zendron <rafael.zendron22@gmail.com>
Date: Wed, 17 Jun 2026 12:27:38 -0300
Subject: [PATCH] fix: isJSONSerializable returns true for null

Fixes #571

The bug was on line 22 where it checked `t === null`,
but typeof never returns "null" (typeof null === "object").

This caused:
1. Dead code: t === null was always false
2. isJSONSerializable(null) threw TypeError accessing null.buffer
3. null was incorrectly identified as not JSON serializable

Fixed by:
- Adding explicit null check before typeof comparison
- Removing t === null from typeof checks (impossible condition)

Tests:
- Added comprehensive unit tests for isJSONSerializable
- All tests pass including null, undefined, primitives, and edge cases
---
 src/utils.ts                    |  5 +++-
 test/isjsonserializable.test.ts | 51 +++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+), 1 deletion(-)
 create mode 100644 test/isjsonserializable.test.ts

diff --git a/src/utils.ts b/src/utils.ts
index a773431b..2e79fc7a 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -18,8 +18,11 @@ export function isJSONSerializable(value: any): boolean {
   if (value === undefined) {
     return false;
   }
+  if (value === null) {
+    return true;
+  }
   const t = typeof value;
-  if (t === "string" || t === "number" || t === "boolean" || t === null) {
+  if (t === "string" || t === "number" || t === "boolean") {
     return true;
   }
   if (t !== "object") {
diff --git a/test/isjsonserializable.test.ts b/test/isjsonserializable.test.ts
new file mode 100644
index 00000000..be088544
--- /dev/null
+++ b/test/isjsonserializable.test.ts
@@ -0,0 +1,51 @@
+import { describe, it, expect } from "vitest";
+import { isJSONSerializable } from "../src/utils.ts";
+
+describe("isJSONSerializable", () => {
+  it("returns true for null", () => {
+    expect(isJSONSerializable(null)).toBe(true);
+  });
+
+  it("returns false for undefined", () => {
+    expect(isJSONSerializable(undefined)).toBe(false);
+  });
+
+  it("returns true for strings", () => {
+    expect(isJSONSerializable("hello")).toBe(true);
+  });
+
+  it("returns true for numbers", () => {
+    expect(isJSONSerializable(42)).toBe(true);
+    expect(isJSONSerializable(0)).toBe(true);
+    expect(isJSONSerializable(-1)).toBe(true);
+    expect(isJSONSerializable(3.14)).toBe(true);
+  });
+
+  it("returns true for booleans", () => {
+    expect(isJSONSerializable(true)).toBe(true);
+    expect(isJSONSerializable(false)).toBe(true);
+  });
+
+  it("returns true for arrays", () => {
+    expect(isJSONSerializable([])).toBe(true);
+    expect(isJSONSerializable([1, 2, 3])).toBe(true);
+    expect(isJSONSerializable([null, undefined])).toBe(true);
+  });
+
+  it("returns true for plain objects", () => {
+    expect(isJSONSerializable({})).toBe(true);
+    expect(isJSONSerializable({ a: 1 })).toBe(true);
+  });
+
+  it("returns false for buffers", () => {
+    expect(isJSONSerializable(new ArrayBuffer(8))).toBe(false);
+  });
+
+  it("returns false for FormData", () => {
+    expect(isJSONSerializable(new FormData())).toBe(false);
+  });
+
+  it("returns false for URLSearchParams", () => {
+    expect(isJSONSerializable(new URLSearchParams())).toBe(false);
+  });
+});
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