PushEvent.data should be NULL for empty payloads

chrome/test/data/push_messaging/service_worker.js

Index: chrome/test/data/push_messaging/service_worker.js
diff --git a/chrome/test/data/push_messaging/service_worker.js b/chrome/test/data/push_messaging/service_worker.js
index e884e899b39348d4e48e9446bfe1e55ebf6c5e63..a338fdc12b67916945a433b11fde0aa64f25debb 100644
--- a/chrome/test/data/push_messaging/service_worker.js
+++ b/chrome/test/data/push_messaging/service_worker.js
@@ -10,6 +10,11 @@
 // "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);