PodFetch: Gpoddersync doesn't sync with AntennaPod

Describe the bug

I’m running PodFetch on a Synology NAS with Docker. I’ve managed to login on AntennaPod, syncing looks successful but no data from Podfetch is being loaded in AntennaPod.

I’ve added a podcast in AntennaPod and I can find that entry in the subscriptions table, but I don’t see it online.

Please let me know how I can provide more debug data.

Reproduction

Antennapod -> login -> force sync: no error, but no data synced

System Info

## Environment
Android version: 14
OS version: 5.10.157-android13-4-00003-gdfb1120f912b-ab10994928
AntennaPod version: 3.1.2
Model: Pixel 6 Pro
Device: raven
Product: raven

## Crash info
Time: 21-11-2023 12:33:19
AntennaPod version: 3.1.2

## StackTrace

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Throwable.getMessage()' on a null object reference
	at de.danoeh.antennapod.fragment.preferences.synchronization.GpodderAuthenticationFragment.lambda$setupLoginView$4(GpodderAuthenticationFragment.java:143)
	at de.danoeh.antennapod.fragment.preferences.synchronization.GpodderAuthenticationFragment.$r8$lambda$PblfpjkWv1kDOd7pkvsz-m1lYHc(GpodderAuthenticationFragment.java:0)
	at de.danoeh.antennapod.fragment.preferences.synchronization.GpodderAuthenticationFragment$$ExternalSyntheticLambda3.accept(R8$$SyntheticClass:0)
	at io.reactivex.internal.observers.CallbackCompletableObserver.onError(CallbackCompletableObserver.java:64)
	at io.reactivex.internal.operators.completable.CompletableObserveOn$ObserveOnCompletableObserver.run(CompletableObserveOn.java:87)
	at io.reactivex.android.schedulers.HandlerScheduler$ScheduledRunnable.run(HandlerScheduler.java:124)
	at android.os.Handler.handleCallback(Handler.java:958)
	at android.os.Handler.dispatchMessage(Handler.java:99)
	at android.os.Looper.loopOnce(Looper.java:205)
	at android.os.Looper.loop(Looper.java:294)
	at android.app.ActivityThread.main(ActivityThread.java:8177)
	at java.lang.reflect.Method.invoke(Native Method)
	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:552)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:971)

### Used Package Manager

n/a

### Validations

- [X] Follow our [Code of Conduct](https://github.com/SamTV12345/.github/blob/main/CODE_OF_CONDUCT.md)
- [X] Read the [Contributing Guide](https://github.com/SamTV12345/.github/blob/main/CONTRIBUTING.md).
- [X] Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
- [X] Check that this is a concrete bug. For Q&A, please open a GitHub Discussion instead.
- [X] The provided reproduction is a [minimal reproducible](https://stackoverflow.com/help/minimal-reproducible-example) of the bug.