fix(fcm): Add V2 config null validation tests and update multicast tests

Author: jonathanedey

src/test/java/com/google/firebase/messaging/MessageTest.java

@@ -1249,6 +1249,21 @@ public void testAndroidNotificationV2WithNegativeVibrateTimings() {
     }
   }
 
+  @Test(expected = NullPointerException.class)
+  public void testAndroidNotificationV2WithNullVibrateTimings() {
+    AndroidNotificationV2.builder().setVibrateTimingsInMillis(null);
+  }
+
+  @Test(expected = NullPointerException.class)
+  public void testAndroidNotificationV2WithNullBodyLocArgs() {
+    AndroidNotificationV2.builder().addAllBodyLocalizationArgs(null);
+  }
+
+  @Test(expected = NullPointerException.class)
+  public void testAndroidNotificationV2WithNullTitleLocArgs() {
+    AndroidNotificationV2.builder().addAllTitleLocalizationArgs(null);
+  }
+
   private static void assertJsonEquals(
       Map<String, Object> expected, Object actual) throws IOException {
     assertEquals(expected, toMap(actual));

src/test/java/com/google/firebase/messaging/MulticastMessageTest.java

@@ -32,6 +32,7 @@ public class MulticastMessageTest {
       .build();
   private static final AndroidConfigV2 ANDROID_V2 = AndroidConfigV2.builder()
       .setCollapseKey("collapseKeyV2")
+      .setBackgroundSync(AndroidBackgroundSyncMessage.builder().build())
       .build();
   private static final ApnsConfig APNS = ApnsConfig.builder()
       .setAps(Aps.builder()