rxjava2 - how to zip Maybe that can be empty? - rx-java2

Question

I am attempting to make 3 web services calls (e.g.: getPhoneNumber, getFirstName, getLastName) and collect the answers into a common object Person. Any of the web services calls can return a Maybe.empty().
When attempting to zip the response together, rxjava2 skips over the zip operation and terminate normally (without having aggregated my answer).
For a simplified example, see below:
#Test
public void maybeZipEmptyTest() throws Exception {
Maybe<Integer> a = Maybe.just(1);
Maybe<Integer> b = Maybe.just(2);
Maybe<Integer> empty = Maybe.empty();
TestObserver<String> observer = Maybe.zip(a, b, empty, (x, y, e) -> {
String output = "test: a "+x+" b "+y+" empty "+e;
return output;
})
.doOnSuccess(output -> {
System.out.println(output);
})
.test();
observer.assertNoErrors();
}
How can we collect empty values within a zip operation instead of having the zip operation skipped/ignored? If this is the wrong pattern to solve this problem, how would you recommend solving this?

Answer 1

For most use cases, leveraging the defaultIfEmpty method is the right way to go.
For representing something which is ultimately optional (doesn't even use default), I used Java 8 Optional type to represent.
For example
#Test
public void maybeZipEmptyTest() throws Exception {
Maybe<Optional<Integer>> a = Maybe.just(Optional.of(1));
Maybe<Optional<Integer>> b = Maybe.just(Optional.of(2));
Maybe<Optional<Integer>> empty = Maybe.just(Optional.empty());
TestObserver<String> observer = Maybe.zip(a, b, empty, (x, y, e) -> {
String output = "test: a "+toStringOrEmpty(x)+" b "+toStringOrEmpty(y)+" empty "+toStringOrEmpty(e);
return output;
})
.doOnSuccess(output -> {
System.out.println(output);
})
.test();
observer.assertNoErrors();
}
private String toStringOrEmpty(Optional<Integer> value){
if(value.isPresent()){
return value.get().toString();
}
else {
return "";
}
}