code:

LiveData<List<Task>> observableTasks = ((MyApp) getApplication())
        .getRepository()
        .loadOutstandingTasksWithNotifications();

Observer<List<Task>> observer = new Observer<List<Task>>() {
    @Override
    public void onChanged(@Nullable List<Task> tasks) {
        if (tasks != null && !tasks.isEmpty()) {
            // do stuff with tasks
        }
        observableTasks.removeObserver(this);
    }
};

observableTasks.observeForever(observer);