PushEvent.data should be NULL for empty payloads

chrome/test/data/push_messaging/service_worker.js

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // The "onpush" event currently understands two values as message payload
 // data coming from the test. Any other input is passed through to the
 // document unchanged.
 //
 // "shownotification" - Display a Web Notification with event.waitUntil().
 // "shownotification-without-waituntil"
 //     - Display a Web Notification without using event.waitUntil().
 this.onpush = function(event) {
+  if (event.data === null) {
+    sendMessageToClients('push', '[NULL]');
+    return;
+  }
+
   var data = event.data.text();
   if (!data.startsWith('shownotification')) {
     sendMessageToClients('push', data);
     return;
   }
 
   var result = registration.showNotification('Push test title', {
     body: 'Push test body',
     tag: 'push_test_tag'
   });
@@ skipping 16 matching lines @@
     'data': data
   });
   clients.matchAll().then(function(clients) {
     clients.forEach(function(client) {
       client.postMessage(message);
     });
   }, function(error) {
     console.log(error);
   });
 }