From 6edc3b572cb934a6f77f6f49952eff1aab759964 Mon Sep 17 00:00:00 2001
From: Matthew Podwysocki <matthewp@microsoft.com>
Date: Tue, 6 Sep 2022 18:46:00 -0400
Subject: [PATCH] [notification hubs] Fix empty registration feed bug (#23121)

---
 .../src/serializers/registrationSerializer.ts    |  6 +++++-
 .../internal/unit/registrationSerializer.spec.ts | 16 ++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/sdk/notificationhubs/notification-hubs/src/serializers/registrationSerializer.ts b/sdk/notificationhubs/notification-hubs/src/serializers/registrationSerializer.ts
index 51258769fbac..858f99fadfc5 100644
--- a/sdk/notificationhubs/notification-hubs/src/serializers/registrationSerializer.ts
+++ b/sdk/notificationhubs/notification-hubs/src/serializers/registrationSerializer.ts
@@ -187,7 +187,11 @@ export const registrationDescriptionParser: RegistrationDescriptionParser = {
    */
   async parseRegistrationFeed(bodyText: string): Promise<RegistrationDescription[]> {
     const xml = await parseXML(bodyText, { includeRoot: true });
-    const results = [];
+    const results: RegistrationDescription[] = [];
+    if (!isDefined(xml.feed.entry)) {
+      return results;
+    }
+
     for (const entry of xml.feed.entry) {
       delete entry.content["$"];
 
diff --git a/sdk/notificationhubs/notification-hubs/test/internal/unit/registrationSerializer.spec.ts b/sdk/notificationhubs/notification-hubs/test/internal/unit/registrationSerializer.spec.ts
index afe9385bbda0..6b8dc24c3917 100644
--- a/sdk/notificationhubs/notification-hubs/test/internal/unit/registrationSerializer.spec.ts
+++ b/sdk/notificationhubs/notification-hubs/test/internal/unit/registrationSerializer.spec.ts
@@ -491,6 +491,14 @@ const REGISTRATION_FEED = `<?xml version="1.0" encoding="utf-8" ?>
   </entry>
 </feed>`;
 
+const EMPTY_REGISTRATION_FEED = `<?xml version="1.0" encoding="utf-8" ?>
+<feed xmlns="http://www.w3.org/2005/Atom">
+  <title type="text">Registrations</title>
+  <id>https://testns.servicebus.windows.net/testhub/registrations/?api-version=2020-06</id>
+  <updated>2022-09-06T20:06:33Z</updated>
+  <link rel="self" href="https://testns.servicebus.windows.net/testhub/registrations/?api-version=2020-06" />
+</feed>`;
+
 describe("parseRegistrationFeed", () => {
   it("should parse a registration feed", async () => {
     const registrations = await registrationDescriptionParser.parseRegistrationFeed(
@@ -509,6 +517,14 @@ describe("parseRegistrationFeed", () => {
     assert.equal(appleRegistration.deviceToken, "{DeviceToken}");
     assert.deepEqual(appleRegistration.tags, ["myTag", "myOtherTag"]);
   });
+
+  it("should parse an empty feed", async () => {
+    const registrations = await registrationDescriptionParser.parseRegistrationFeed(
+      EMPTY_REGISTRATION_FEED
+    );
+
+    assert.equal(registrations.length, 0);
+  });
 });
 
 describe("serializeRegistrationDescription", () => {