Completable swallows OnErrorNotImplementedException

[kotucz]

In the following case, the IllegalStateException should cause OnErrorNotImplementedException, because subscribe() has no onError handler specified.

        Completable.fromCallable(() -> {
            throw new IllegalStateException("FOO");
        })
            .toSingleDefault(1)
            .subscribe();

In the related issue #3726 and PR #3733, similar problem was solved, that the exception was propagated to the thread exception handler. For example it works correctly in the following snippet and the OnErrorNotImplementedException delivered.

        Completable.fromCallable(() -> {
            throw new IllegalStateException("FOO");
        })
            .subscribe();

Maybe more of the usages of the toNpe() shall be replaced with deliverUncaughtException()?

[akarnokd]

Relying on OnErrorNotImplementedException being thrown is a fragile position but for consistency, PR welcome.

[kotucz]

Not relying on it. But it hides programming errors. The app then behaves incorrectly instead of crashing.