Getting empty users list from viewModel class

Question

I am trying get users list from Firebase. I use repository and viewmodel. I am newcomer in the clean architecture and I think, that I made error , when have made viewModel method.

`class UserRepository {
private var usersList: ArrayList<User>? = ArrayList()
fun readUsers(): ArrayList<User> {
    var firebaseUser: FirebaseUser? = FirebaseAuth.getInstance().currentUser
    var databaseReference: DatabaseReference =
        FirebaseDatabase.getInstance().getReference("Users")

    databaseReference.addValueEventListener(object : ValueEventListener {
        override fun onDataChange(dataSnapshot: DataSnapshot) {
            usersList?.clear()
            for (data: DataSnapshot in dataSnapshot.children) {
                val user: User? = data.getValue(User::class.java)
                if (!user?.id.equals(firebaseUser?.uid)) {
                    usersList?.add(user!!)
                }
            }
        }

        override fun onCancelled(error: DatabaseError) {
            // Failed to read value
        }
    })

    return usersList!!
}

}`

when I am debugging I see that usrlist is not empty

class UserViewModel(application: Application) : AndroidViewModel(application){

    private var userRepository: UserRepository? = UserRepository()
    private var mutableLiveData: MutableLiveData<List<User>>? = MutableLiveData()

    init {
        mutableLiveData?.value=userRepository?.readUsers()
    }

    fun getAllUsers(): MutableLiveData<List<User>>? {
        return mutableLiveData
    }
}

and in fragment I call:

override fun onActivityCreated(savedInstanceState: Bundle?) {
    super.onActivityCreated(savedInstanceState)
    userViewModel = ViewModelProvider(this)[UserViewModel::class.java]
    userViewModel?.getAllUsers()?.observe(viewLifecycleOwner,
        { t ->
            userAdapter = UserAdapter(requireContext(), t!!, false)
            recyclerView?.adapter = userAdapter
        })
}

I dont understand, why firstly calls init() from ViewModel.class then getAllUsers() from ViewModel.class then onActivityCreated(savedInstanceState: Bundle?) from fragment and then calls readUsers() from repository???