Android 当试图将错误传播到Observer.onError时，如何处理引发的异常？

我用RxJava、RxAndroid和rx2创建了这个应用程序。我对第2条的询问：

@POST("auth/sign_in")
Observable<Response<AccountEntity>> signIn(@Header("email") String email, @Header("password") String password);

public Observable<AccessToken> signIn(String user, String pass) {
    return netService.signIn(user, pass).flatMap(new Func1<Response<AccountEntity>, Observable<AccessToken>>() {
        @Override
        public Observable<AccessToken> call(final Response<AccountEntity> accountEntityResponse) {

            AccountEntity accountEntity = accountEntityResponse.body();
            diskAccountDataStore.createAccount(accountToAccountEntityMapper.reverseMap(accountEntity)).subscribe();

            return Observable.create(new Observable.OnSubscribe<AccessToken>() {
                @Override
                public void call(Subscriber<? super AccessToken> subscriber) {
                    AccessToken accessToken = new AccessToken.AccesTokenBuilder()
                            .accessToken(accountEntityResponse.headers().get(AccessToken.ACCESS_TOKEN))
                            .tokenType(accountEntityResponse.headers().get(AccessToken.TOKEN_TYPE))
                            .client(accountEntityResponse.headers().get(AccessToken.CLIENT))
                            .expiry(accountEntityResponse.headers().get(AccessToken.EXPIRY))
                            .uid(accountEntityResponse.headers().get(AccessToken.UID))
                            .build();

                    subscriber.onNext(accessToken);
                }
            });
        }
    });
}

private final class SignInSubscriber extends DefaultSubscriber<AccessToken> {
    @Override
    public void onCompleted() {
        super.onCompleted();
    }

    @Override
    public void onError(Throwable e) {
        super.onError(e);
        if (e instanceof HttpException) {
            ResponseBody responseBody = ((HttpException) e).response().errorBody();
            getView().signInError(getErrorMessage(responseBody));
        } else if (e instanceof SocketTimeoutException)
            getView().signInError("Connection timeout");
        else if (e instanceof IOException)
            getView().signInError("Network error");
        else
            getView().signInError("Wrong credentials");

    }

    @Override
    public void onNext(AccessToken token) {
        super.onNext(token);
        getView().signInSuccess(token);
    }

    private String getErrorMessage(ResponseBody responseBody) {
        try {
            JSONObject jsonObject = new JSONObject(responseBody.string());
            return jsonObject.getString("errors");
        } catch (Exception e) {
            return e.getMessage();
        }
    }
}

FATAL EXCEPTION: main
Process: com.app, PID: 26813
java.lang.IllegalStateException: Fatal Exception thrown on Scheduler.Worker thread.
at    rx.android.schedulers.LooperScheduler$ScheduledAction.run(LooperScheduler.java:114)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7224)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
 Caused by: rx.exceptions.OnErrorFailedException: Error occurred when trying to propagate error to Observer.onError
at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:187)
at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:115)
at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.checkTerminated(OperatorObserveOn.java:273)
at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.call(OperatorObserveOn.java:216)
at rx.android.schedulers.LooperScheduler$ScheduledAction.run(LooperScheduler.java:107)
at android.os.Handler.handleCallback(Handler.java:739) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:158) 
at android.app.ActivityThread.main(ActivityThread.java:7224) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 
 Caused by: rx.exceptions.CompositeException: 2 exceptions occurred. 
at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:187) 
at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:115) 
at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.checkTerminated(OperatorObserveOn.java:273) 
at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.call(OperatorObserveOn.java:216) 
at rx.android.schedulers.LooperScheduler$ScheduledAction.run(LooperScheduler.java:107) 
at android.os.Handler.handleCallback(Handler.java:739) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:158) 
at android.app.ActivityThread.main(ActivityThread.java:7224) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 
 Caused by: rx.exceptions.CompositeException$CompositeExceptionCausalChain: Chain of Causes for CompositeException In Order Received =>
at android.util.Log.getStackTraceString(Log.java:508)
at com.android.internal.os.RuntimeInit.Clog_e(RuntimeInit.java:60)
at com.android.internal.os.RuntimeInit.access$200(RuntimeInit.java:44)
at com.android.internal.os.RuntimeInit$UncaughtHandler.uncaughtException(RuntimeInit.java:92)
at java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:693)
at java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:690)
at rx.android.schedulers.LooperScheduler$ScheduledAction.run(LooperScheduler.java:118)
at android.os.Handler.handleCallback(Handler.java:739) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:158) 
at android.app.ActivityThread.main(ActivityThread.java:7224) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 
 Caused by: java.net.SocketTimeoutException
at java.net.PlainSocketImpl.read(PlainSocketImpl.java:484)
at java.net.PlainSocketImpl.access$000(PlainSocketImpl.java:37)
at java.net.PlainSocketImpl$PlainSocketInputStream.read(PlainSocketImpl.java:237)
at okio.Okio$2.read(Okio.java:139)
at okio.AsyncTimeout$2.read(AsyncTimeout.java:237)
at okio.RealBufferedSource.indexOf(RealBufferedSource.java:345)
at okio.RealBufferedSource.readUtf8LineStrict(RealBufferedSource.java:217)
at okio.RealBufferedSource.readUtf8LineStrict(RealBufferedSource.java:211)
at okhttp3.internal.http1.Http1Codec.readResponseHeaders(Http1Codec.java:189)
at okhttp3.internal.http.CallServerInterceptor.intercept(CallServerInterceptor.java:75)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:92)
at okhttp3.internal.connection.ConnectInterceptor.intercept(ConnectInterceptor.java:45)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:92)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:67)
at okhttp3.internal.cache.CacheInterceptor.intercept(CacheInterceptor.java:93)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:92)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:67)
at okhttp3.internal.http.BridgeInterceptor.intercept(BridgeInterceptor.java:93)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:92)
at okhttp3.internal.http.RetryAndFollowUpInterceptor.intercept(RetryAndFollowUpInterceptor.java:120)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:92)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:67)
at okhttp3.RealCall.getResponseWithInterceptorChain(RealCall.java:185)
at okhttp3.RealCall.execute(RealCall.java:69)
at retrofit2.OkHttpCall.execute(OkHttpCall.java:180)
at retrofit2.adapter.rxjava.RxJavaCallAdapterFactory$RequestArbiter.request(RxJavaCallAdapterFactory.java:171)
at rx.Subscriber.setProducer(Subscriber.java:211)
at rx.interna