fix(router): use default behavior for no-content handling

Author: pi0

src/router.ts

@@ -6,7 +6,6 @@ import {
 import type { HTTPMethod, EventHandler } from "./types";
 import { createError } from "./error";
 import { eventHandler, toEventHandler } from "./event";
-import { setResponseStatus } from "./utils";
 
 export type RouterMethod = Lowercase<HTTPMethod>;
 const RouterMethods: RouterMethod[] = [
@@ -151,8 +150,7 @@ export function createRouter(opts: CreateRouterOptions = {}): Router {
     // Call handler
     return Promise.resolve(handler(event)).then((res) => {
       if (res === undefined && (opts.preemptive || opts.preemtive)) {
-        setResponseStatus(event, 204);
-        return "";
+        return null; // Send empty content
       }
       return res;
     });