fix (firebase#739)

Author: charlotteliang

Firebase/Messaging/FIRMessaging.m

@@ -484,7 +484,7 @@ - (void)setAutoInitEnabled:(BOOL)autoInitEnabled {
   [_messagingUserDefaults setBool:autoInitEnabled
                            forKey:kFIRMessagingUserDefaultsKeyAutoInitEnabled];
   if (!isFCMAutoInitEnabled && autoInitEnabled) {
-    self.defaultFcmToken = [self FCMToken];
+    self.defaultFcmToken = [self.instanceIDProxy token];
   }
 }
 
@@ -834,7 +834,7 @@ - (FIRMessagingNetworkStatus)networkType {
 #pragma mark - Notifications
 
 - (void)didReceiveDefaultInstanceIDToken:(NSNotification *)notification {
-  if (![notification.object isKindOfClass:[NSString class]]) {
+  if (notification.object && ![notification.object isKindOfClass:[NSString class]]) {
     FIRMessagingLoggerDebug(kFIRMessagingMessageCodeMessaging015,
                             @"Invalid default FCM token type %@",
                             NSStringFromClass([notification.object class]));