Uncaught (in promise) DOMException: Registration f

Question

Im trying to implement push notification using Polymer. I followed this link and was able to get the service worker to be registered. I got the following comments of the Javascript console.

Service Worker is ready :^) ServiceWorkerRegistration

But I also received this error.

Uncaught (in promise) DOMException: Registration failed - manifest empty or missing

Note:

<link rel="manifest" href="manifest.json">

is already in my index.html. Since Im using Google App Engine, in my app.yaml I have add the following as well

url: /manifest.json
  static_files: templates/manifest.json
  upload: templates/manifest.json

And if I try localhost:8080/manifest.json, my manifest json is displayed on the browser. Im unable to get it working. Please provide some help, suggestions to check if manifest.json is actually accessible in my index.html