Why am I seeing a "RegisterForPushNotifications: token is empty" error after updating the SDK?

This message means your app called a Pushwoosh registration method with a null or empty push token, so the SDK refused to act on it.

Where it comes from

Pushwoosh.getInstance().registerExistingToken(token, callback) checks the token before doing anything else. On an empty value it logs token is empty at warning level and does not proceed with registration. Note that:

• The callback is invoked, with a failed result carrying a RegisterForPushNotificationsException("token is empty") — check result.isSuccess() / getException() rather than assuming the callback never fires.
• Nothing is sent to Pushwoosh, so the device is not registered and will not receive pushes.

This only affects registerExistingToken(), the method used when your app obtains the FCM/APNs token itself and hands it to Pushwoosh. The normal registerForPushNotifications() flow requests the token from the push service on its own and is not affected.

How to fix it

1. Call registerExistingToken() only from inside the callback that delivers the token (for example FirebaseMessaging getToken() success, onNewToken(), or didRegisterForRemoteNotificationsWithDeviceToken on iOS) — never at app start.
2. Guard the call with a null/empty check of your own so the SDK is not invoked with a missing value.
3. If you do not need to manage the token yourself, drop registerExistingToken() and use Pushwoosh.getInstance().registerForPushNotifications(callback) instead; that path reports success and failure through its callback.
4. If the push service itself never returns a token, the problem is upstream — check that your Firebase / APNs configuration matches the project configured in Pushwoosh.