static Scheduler callRequireNonNull(Callable<Scheduler> s) {
        try {
            Scheduler scheduler = s.call();
            if (scheduler == null) {
                throw new NullPointerException("Scheduler Callable returned null");
            }
            return scheduler;
        } catch (Throwable ex) {
            throw Exceptions.propagate(ex);
        }
    }
Removes all handlers and resets the default behavior.
android/android_framework/base/src/main/java/rx2/android/plugins/RxAndroidPlugins.java