NullPointerException for empty preferences.

With the change on Rx2 that null cannot be emitted, the simples code implementation like below crashes with NPE (stack below).

As far as I could find, it should be easy to fix. The call that triggers a initial load on RealPreferences@31 (.startWith("<init>")) should only happen if(preferences.containsKey(key)

        RxSharedPreferences rxPref = RxSharedPreferences.create(getSharedPreferences("myprefs", 0));
        Preference<String> rxString = rxPref.getString("string");
        rxString.asObservable().subscribe(new Consumer<String>() {
            @Override
            public void accept(String s) throws Exception {

            }
        });

java.lang.NullPointerException: The mapper function returned a null value.
at io.reactivex.internal.functions.ObjectHelper.requireNonNull(ObjectHelper.java:39)
at io.reactivex.internal.operators.observable.ObservableMap$MapObserver.onNext(ObservableMap.java:58)
at io.reactivex.internal.operators.observable.ObservableConcatMap$ConcatMapDelayErrorObserver.drain(ObservableConcatMap.java:462)
at io.reactivex.internal.operators.observable.ObservableConcatMap$ConcatMapDelayErrorObserver.onSubscribe(ObservableConcatMap.java:325)
at io.reactivex.internal.operators.observable.ObservableFromArray.subscribeActual(ObservableFromArray.java:29)
at io.reactivex.Observable.subscribe(Observable.java:10514)
at io.reactivex.internal.operators.observable.ObservableConcatMap.subscribeActual(ObservableConcatMap.java:54)
at io.reactivex.Observable.subscribe(Observable.java:10514)
at io.reactivex.internal.operators.observable.ObservableMap.subscribeActual(ObservableMap.java:32)
at io.reactivex.Observable.subscribe(Observable.java:10514)
at io.reactivex.Observable.subscribe(Observable.java:10500)
at io.reactivex.Observable.subscribe(Observable.java:10403)

[PaulWoitaschek]

Exatlcy what I described in #49

Well then you should catch that error and throw an appropriate one. I think it’s appropriate to make the default value strictly NonNull and throw an NPE when the default value is null. Thats consistent to RxJava 2. If people do not have a default value they should use an Optional.

[budius]

The code snippet I showed is a simplified version of my code. My code in reality is from a custom object that is created from a GsonPreferenceAdapter, that come from a builder. For my current workaround I’ve added a default empty object (as you suggest) and check/filter if(object.apiKey == null).

I understand and agree that might not be the right solution, as it doesn’t fix the case when u clear the preference value/have a null value.

But still, a straight forward crash like this is not the best behavior, and there should be something that can be done to improve this great library =)

So I’ll suggest to maybe remove the rxPref.getString("string"); method and leave just rxPref.getString("string", "some default"); and internally null check that default can’t be null and throw a properly descriptive error message.