Unexpected NullPointerException when using LiveData in ViewModel with Room Database
I'm confused about I'm attempting to set up I'm encountering a `NullPointerException` when trying to observe a `LiveData` object in my `ViewModel`... I'm using Room for my database and the Android Architecture Components, specifically `ViewModel` and `LiveData`. The issue arises when I try to access the `LiveData` from my Fragment, which sometimes returns null. Here's a simplified version of my code: ```kotlin class MyViewModel(application: Application) : AndroidViewModel(application) { private val repository: MyRepository = MyRepository(application) val myData: LiveData<List<MyEntity>> = repository.getAllData() } ``` In the repository, I fetch data from the Room database: ```kotlin class MyRepository(application: Application) { private val myDao: MyDao = MyDatabase.getDatabase(application).myDao() fun getAllData(): LiveData<List<MyEntity>> { return myDao.getAllMyEntities() } } ``` And here’s how I observe the `LiveData` in my Fragment: ```kotlin class MyFragment : Fragment() { private lateinit var viewModel: MyViewModel override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View { val view = inflater.inflate(R.layout.fragment_my, container, false) viewModel = ViewModelProvider(this).get(MyViewModel::class.java) viewModel.myData.observe(viewLifecycleOwner, Observer { data -> // This line throws NullPointerException sometimes updateUI(data) }) return view } } ``` The `MyDao` interface looks like this: ```kotlin @Dao interface MyDao { @Query("SELECT * FROM my_entity") fun getAllMyEntities(): LiveData<List<MyEntity>> } ``` I believe the `LiveData` should never be null since it should initialize with an empty list if there is no data, but I occasionally see `NullPointerException` when `updateUI(data)` is called. I've tried adding logging to see if `data` is ever null, and it appears to be the case, but I can't figure out why. I’ve also made sure to return an empty list in the DAO query method. Here’s the relevant part of my database implementation: ```kotlin @Database(entities = [MyEntity::class], version = 1) abstract class MyDatabase : RoomDatabase() { abstract fun myDao(): MyDao companion object { @Volatile private var instance: MyDatabase? = null fun getDatabase(context: Context): MyDatabase { return instance ?: synchronized(this) { val newInstance = Room.databaseBuilder(context.applicationContext, MyDatabase::class.java, "my_database" ).build() instance = newInstance newInstance } } } } ``` I've tried running on both emulator and a physical device and saw the same behavior. Could this be an issue with how Room initializes the `LiveData`, or am I potentially missing something in the lifecycle of my ViewModel and Fragment? Any insights would be greatly appreciated! Could this be a known issue? I recently upgraded to Kotlin 3.11. Any examples would be super helpful.