Another approach where EventLiveData contains a reference to its lifecycle.

EventLiveData.java

public class EventLiveData extends LiveData<Object> {

    private final int mSubject;
    private final LifecycleRegistryOwner mLifecycle;

    public EventLiveData(@LiveDataBus.Subject int subject, @NonNull LifecycleRegistryOwner lifecycle) {
        mSubject = subject;
        mLifecycle = lifecycle;
    }

    public void update(Object object) {
        setValue(object);
    }

    @Override
    public void removeObserver(Observer<Object> observer) {
        super.removeObserver(observer);
        if (!hasObservers()) {
            LiveDataBus.unregister(mSubject, mLifecycle);
        }
    }
}