fix(handler): handle invalid input in handler.fetch()

handler.fetch(null), handler.fetch(undefined), and handler.fetch(123)
would throw an unhandled TypeError instead of returning an error response.

Now validates the input before processing and returns a 500 response
with the error details for invalid inputs.

Closes #1254

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: productdevbook

src/handler.ts

@@ -107,6 +107,9 @@ function handlerWithFetch<
   }
   return Object.assign(handler, {
     fetch: (req: ServerRequest | URL | string): Promise<Response> => {
+      if (!req || (typeof req !== "string" && typeof req !== "object")) {
+        return Promise.resolve(toResponse(new TypeError("Invalid fetch input", { cause: req }), new H3Event(new Request("http://_"))));
+      }
       if (typeof req === "string") {
         req = new URL(req, "http://_");
       }

test/handler.test.ts

@@ -39,6 +39,26 @@ describe("handler.ts", () => {
     });
   });
 
+  describe("handler.fetch with invalid input", () => {
+    it("returns 500 response for null input", async () => {
+      const handler = defineHandler(() => "ok");
+      const res = await handler.fetch(null as any);
+      expect(res.status).toBe(500);
+    });
+
+    it("returns 500 response for undefined input", async () => {
+      const handler = defineHandler(() => "ok");
+      const res = await handler.fetch(undefined as any);
+      expect(res.status).toBe(500);
+    });
+
+    it("returns 500 response for numeric input", async () => {
+      const handler = defineHandler(() => "ok");
+      const res = await handler.fetch(123 as any);
+      expect(res.status).toBe(500);
+    });
+  });
+
   describe("dynamicEventHandler", () => {
     it("should call the initial handler if set", async () => {
       const initialHandler = vi.fn(async (_: H3Event) => "initial");