Fatal Exception: java.lang.NullPointerException: Attempt to invoke interface method 'rf.a com.microsoft.signalr.Transport.stop()' on a null object reference
       at com.microsoft.signalr.HubConnection.lambda$stop$16(HubConnection.java:448)
       at io.reactivex.rxjava3.internal.observers.CallbackCompletableObserver.onComplete(CallbackCompletableObserver.java:53)
       at io.reactivex.rxjava3.internal.operators.completable.CompletableOnErrorComplete$OnError.onError(CompletableOnErrorComplete.java:64)
       at io.reactivex.rxjava3.subjects.CompletableSubject.onError(CompletableSubject.java:126)
       at com.microsoft.signalr.HubConnection.lambda$start$12(HubConnection.java:358)
       at io.reactivex.rxjava3.internal.observers.CallbackCompletableObserver.onError(CallbackCompletableObserver.java:64)
       at io.reactivex.rxjava3.internal.operators.single.SingleFlatMapCompletable$FlatMapCompletableObserver.onError(SingleFlatMapCompletable.java:97)
       at io.reactivex.rxjava3.internal.observers.ResumeSingleObserver.onError(ResumeSingleObserver.java:51)
       at io.reactivex.rxjava3.internal.operators.single.SingleFlatMap$SingleFlatMapCallback.onError(SingleFlatMap.java:91)
       at io.reactivex.rxjava3.internal.operators.single.SingleMap$MapSingleObserver.onError(SingleMap.java:70)
       at io.reactivex.rxjava3.subjects.SingleSubject.onError(SingleSubject.java:153)
       at com.microsoft.signalr.DefaultHttpClient$2.onFailure(DefaultHttpClient.java:149)
       at okhttp3.internal.connection.RealCall$AsyncCall.run(RealCall.kt:525)
       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:644)
       at java.lang.Thread.run(Thread.java:1012)

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        val hubConnection: HubConnection = HubConnectionBuilder
            .create("https://someInvalidUrl")
            .build()

        hubConnection.start()
            .subscribe({
                Log.d("SomeTag", "Successfully connected to Webserver")
            }, { e ->
                Log.e("SomeTag", "Failed to start connection: ${e.message}")
            })

        hubConnection.stop()  // <------ this leads to app crash
            .subscribe({ 
                Log.d("SomeTag", "HubConnection Stop Success")
            }, {
                Log.e("SomeTag", "HubConnection Stop Failed: ${it.message}")
            })
    }
}