使用分页库时，新的LivePagedListBuilder返回NullPointerException

Question

我正在使用paging library从房间获取recyclerview物品，尝试尝试新的新LivePagedListBuilder时出现nullPointerException，这是我的代码：

Activity.class

    requestViewModel.request.getListenTo().observe(this,listenTo->{
        if(listenTo == RequestViewModel.LISTEN_TO_ALL_RANDOM){
            requestViewModel.getMedicalEntities().observe(this,pagedListEntity->{
                entityRecyclerAdapter.submitList(pagedListEntity);
            });
        }
    });


    /**
     * Search Text Observing
     */
    requestViewModel.request.getSearchText().observe(this,searchText->{
        if(searchText.length()>0){
            requestViewModel.request.setListenTo(RequestViewModel.LISTEN_TO_SEARCH);
            entityRecyclerAdapter.submitList(requestViewModel.makeFilterBySearch(searchText).getValue());

        }else {
            requestViewModel.request.setListenTo(RequestViewModel.LISTEN_TO_ALL_RANDOM);
        }
    });

RequestViewModel.class

private LiveData<PagedList<MedicalEntity>> medicalEntities;
private LiveData<PagedList<MedicalEntity>> searchEntitiesDataSource;



public RequestViewModel(AppRepository appRepository) {
    request = new Request();
    request.setListenTo(LISTEN_TO_ALL_RANDOM);

    medicalEntities = new LivePagedListBuilder<>(appRepository.getRandomEntities(),3)
            .setInitialLoadKey(0)
            .build();
}

public LiveData<PagedList<MedicalEntity>> makeFilterBySearch(String search){
    searchEntitiesDataSource = new LivePagedListBuilder<>(appRepository.getEntitiesBySearch(search),3)
            .build();

    return searchEntitiesDataSource;
}



public LiveData<PagedList<MedicalEntity>> getMedicalEntities() {
    return medicalEntities;
}

Repository.class

  public DataSource.Factory<Integer, MedicalEntity> getRandomEntities() {
    initializeEntitiesData();
    return entityDao.getEntities();
}

public DataSource.Factory<Integer,MedicalEntity> getEntitiesBySearch(String searchText) {
    return entityDao.getEntitiesBySearch("%"+searchText+"%");
}

我收到NullPointerException错误

12-16 19:10:01.969 26717-26717/com.banquemisr.www.bmmedical E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.banquemisr.www.bmmedical, PID: 26717
    java.lang.NullPointerException
        at com.banquemisr.www.bmmedical.ui.requests.RequestViewModel.makeFilterBySearch(RequestViewModel.java:36)
        at com.banquemisr.www.bmmedical.ui.requests.RequestsActivity.lambda$onCreate$2(RequestsActivity.java:106)

你能帮我吗？