Android：为什么在尝试分配给变量时不运行Transformation.map？

我正在尝试在项目中使用Firebase API，但视图模型中Transformations.map的变量authenticationState无法运行。我在这里一直在关注Google的教程（链接转到该项目的ViewModel）。

我希望以后可以将Transformations.map代码添加到FirebaseUserLiveData文件中，但似乎无法弄清楚为什么它无法运行。

FirebaseUserLiveData

class FirebaseUserLiveData: LiveData<FirebaseUser?>() {

    private val firebaseAuth = FirebaseAuth.getInstance()
    private val authStateListener = FirebaseAuth.AuthStateListener { firebaseAuth ->
        value = firebaseAuth.currentUser
    }


    override fun onActive() {
        firebaseAuth.addAuthStateListener { authStateListener }
    }

    override fun onInactive() {
        firebaseAuth.removeAuthStateListener(authStateListener)
    }
}

SearchMovieFragmentViewModel

class SearchMovieFragmentViewModel : ViewModel() {

    enum class AuthenticationState {
        AUTHENTICATED, UNAUTHENTICATED, INVALID_AUTHENTICATION
    }

    var authenticationState = Transformations.map(FirebaseUserLiveData()) { user ->
        Log.d("TEST", "in the state function")
        if (user != null) {
            AuthenticationState.AUTHENTICATED
        } else {
            AuthenticationState.UNAUTHENTICATED
        }
    }

SearchMovieFragment

class SearchMovieFragment : Fragment(), MovieSearchItemViewModel {

    companion object {
        fun newInstance() = SearchMovieFragment()
    }

    private lateinit var searchMovieFragmentViewModel: SearchMovieFragmentViewModel
    private lateinit var binding: SearchMovieFragmentBinding
    private lateinit var movieRecyclerView: RecyclerView

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {

        binding = DataBindingUtil.inflate(inflater, R.layout.search_movie_fragment, container, false)
        searchMovieFragmentViewModel = ViewModelProvider(this).get(SearchMovieFragmentViewModel::class.java)
        binding.lifecycleOwner = this
        binding.viewmodel = searchMovieFragmentViewModel

        binding.signOutButton.setOnClickListener {
            AuthUI.getInstance().signOut(requireContext())
        }

        searchMovieFragmentViewModel.authenticationState.observe(viewLifecycleOwner, Observer { state ->
            when (state) {
                AUTHENTICATED -> searchMovieFragmentViewModel.signedIn = View.VISIBLE
                UNAUTHENTICATED -> searchMovieFragmentViewModel.signedIn = View.GONE
            }
        })
        return binding.root
    }
}