java.lang.NullPointerException: The mapper function returned a null value.

[sunzhk]

RxJava throw an exception when I use RxCache + RxJava2 + Retrofit2

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$MapObserver.onNext(ObservableMap.java:59)
    at io.reactivex.internal.operators.observable.ObservableScalarXMap$ScalarDisposable.run(ObservableScalarXMap.java:248)
    at io.reactivex.internal.operators.observable.ObservableJust.subscribeActual(ObservableJust.java:35)
    at io.reactivex.Observable.subscribe(Observable.java:12055)
    at io.reactivex.internal.operators.observable.ObservableMap.subscribeActual(ObservableMap.java:33)
    at io.reactivex.Observable.subscribe(Observable.java:12055)
    at io.reactivex.internal.operators.observable.ObservableDefer.subscribeActual(ObservableDefer.java:39)
    at io.reactivex.Observable.subscribe(Observable.java:12055)
    at io.reactivex.internal.operators.observable.ObservableSubscribeOn$SubscribeTask.run(ObservableSubscribeOn.java:96)
    at io.reactivex.Scheduler$DisposeTask.run(Scheduler.java:579)
    at io.reactivex.internal.schedulers.ScheduledRunnable.run(ScheduledRunnable.java:66)
    at io.reactivex.internal.schedulers.ScheduledRunnable.call(ScheduledRunnable.java:57)
    at java.util.concurrent.FutureTask.run(FutureTask.java:237)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:152)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:265)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
    at java.lang.Thread.run(Thread.java:841)

I use io.reactivex.rxjava2:rxjava:2.1.14-RC1, and this problem also appeared when I used io.reactivex.rxjava2:rxjava:2.1.6

[qingmei2]

@sunzhk

These error logs are not enough，could you please put your codes at here? 😄