public void ifNotHandled(@NonNull final Consumer<T> consumer) {
        if (hasBeenHandled) {
            return;
        }
        hasBeenHandled = true;
        consumer.accept(content);
    }
Invoke the given consumer, if event was not yet handled

@param consumer action which should be performed on the given event content
main/src/main/java/cgeo/geocaching/utils/livedata/Event.java