fixed cors response body

index.js

@@ -298,7 +298,7 @@ class Router {
         const request = { headers: event.request.headers, method: event.request.method, url: event.request.url, event: event }
         request.params = []
         if (request.method === 'OPTIONS' && Object.keys(this.corsConfig).length) {
-            return new Response('', {
+            return new Response(null, {
                 headers: {
                     'Access-Control-Allow-Origin': this.corsConfig.allowOrigin,
                     'Access-Control-Allow-Methods': this.corsConfig.allowMethods,