Rx Observable onErrorReturnItem - rx-java2

Question

I have following code
public Observable<Map<Integer, String>> getMultipleCitiesName(List<Integer> cityIds) {
Observable<Map<Integer, String>> observable = Observable.create(s -> {
try {
System.out.println("getMultipleCitiesName ==="+Thread.currentThread().getName());
List<String> cityIdsString = new ArrayList<>();
for (Integer cityId : cityIds) {
cityIdsString.add(cityId.toString());
}
MultiValueMap<String, String> formParams = new LinkedMultiValueMap<>();
formParams.put("cityIds[]", cityIdsString);
// Call the Location Client to call the API
Response<Map<Integer, String>> response = locationClient.getMultipleCitiesName(formParams);
s.onNext(response.getData());
} catch (Exception e) {
System.out.println("Inside Exception CITY NEW");
s.onError(e);
}
s.onComplete();
});
observable.onErrorReturnItem(new HashMap<>());
return observable;
}
Another stateObs.. same code
then
Observable<Map<Integer, String>> cityNamesObser = locationMediator.getMultipleCitiesName(cityIds);
Observable<Map<Integer, String>> stateNamesObs = locationMediator.getMultipleStatesName(stateIds);
Observable<Map<String, Map<Integer, String>>> zip = Observable.zip(
cityNamesObser,
stateNamesObs,
(cityNamesMap, stateNamesMap) -> {
System.out.println("Zipiing in Thread==="+Thread.currentThread().getName());
Map<String, Map<Integer, String>> result = new HashMap<>();
result.put("cityNames", cityNamesMap);
result.put("stateNames", stateNamesMap);
return result;
});
zip.blockingSubscribe(r -> {
System.out.println("Zip Subscribe in Thread==="+Thread.currentThread().getName());
System.out.println(r);
}, e->{
System.out.println("On Error zip");
});
}
Now the issue, observable.onErrorReturnItem is not working. Not working meaning it is throwing errror instead of returing blank hashmap
But If I change my code to
Observable<Map<Integer, String>> cityNamesObser = locationMediator.getMultipleCitiesName(cityIds).onErrroReturnItem(Blank Map);
Observable<Map<Integer, String>> stateNamesObs = locationMediator.getMultipleStatesName(stateIds).onErrroReturnItem(Blank Map);
Then it is working fine, meaning zip is returing blank hashmap with two keys cityNames and stateNames
Why is that? And do I make ny code work?
Ideally what I want to do is to return blank hashMap if any of my cityObs / stateObs gets failed. For that I want to trigger onError in case of Exception and attached onErrorReturnItem to Observable.