concatMapEager blows up on null values

[Petikoch]

While flatMap and concatMap are fine with flattening null values, concatMapEager blows up.

import rx.Observable;

public class RxJavaNullValueTolerance {

    public static void main(String[] args) {
        Observable.just("just me")
                .flatMap(nextString -> Observable.just(null))
                .subscribe(nextObject -> System.out.println("Got: " + nextObject));
        System.out.println("flatMap is fine with null values");

        Observable.just("just me")
                .concatMap(nextString -> Observable.just(null))
                .subscribe(nextObject -> System.out.println("Got: " + nextObject));
        System.out.println("concatMap is fine with null values");

        Observable.just("just me")
                .concatMapEager(nextString -> Observable.just(null))
                .subscribe(nextObject -> System.out.println("Got: " + nextObject));
        System.out.println("concatMapEager is fine with null values");
    }
}

(RxJava 1.1.0)

Output:

Got: null
flatMap is fine with null values
Got: null
concatMap is fine with null values
Exception in thread "main" rx.exceptions.OnErrorNotImplementedException: null elements not allowed
    at rx.Observable$27.onError(Observable.java:7923)
    at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:159)
    at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:120)
    at rx.internal.operators.OperatorEagerConcatMap$EagerOuterSubscriber.drain(OperatorEagerConcatMap.java:216)
    at rx.internal.operators.OperatorEagerConcatMap$EagerInnerSubscriber.onError(OperatorEagerConcatMap.java:302)
    at rx.Observable.unsafeSubscribe(Observable.java:8105)
    at rx.internal.operators.OperatorEagerConcatMap$EagerOuterSubscriber.onNext(OperatorEagerConcatMap.java:144)
    at rx.internal.util.ScalarSynchronousObservable$1.call(ScalarSynchronousObservable.java:46)
    at rx.internal.util.ScalarSynchronousObservable$1.call(ScalarSynchronousObservable.java:35)
    at rx.Observable$2.call(Observable.java:162)
    at rx.Observable$2.call(Observable.java:154)
    at rx.Observable.subscribe(Observable.java:8191)
    at rx.Observable.subscribe(Observable.java:8158)
    at rx.Observable.subscribe(Observable.java:7914)
    at RxJavaNullValueTolerance.main(RxJavaNullValueTolerance.java:18)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
Caused by: java.lang.NullPointerException: null elements not allowed
    at rx.internal.util.unsafe.SpscArrayQueue.offer(SpscArrayQueue.java:104)
    at rx.internal.operators.OperatorEagerConcatMap$EagerInnerSubscriber.onNext(OperatorEagerConcatMap.java:294)
    at rx.internal.util.ScalarSynchronousObservable$1.call(ScalarSynchronousObservable.java:46)
    at rx.internal.util.ScalarSynchronousObservable$1.call(ScalarSynchronousObservable.java:35)
    at rx.Observable.unsafeSubscribe(Observable.java:8098)
    ... 14 more

This is IMO critical, since these three operators are closely related and often replaced thru each other, depending on the concrete "flattening" requirements.

[Petikoch]

@akarnokd what do you think about this one? Best regards, Peti

[akarnokd]

Yes, this is yet another oversight in eager concatMap. I'll post the fix soon.

[Petikoch]

@akarnokd , thanks a lot!

[zsxwing]

Fixed in #3630