How to transform LiveData<List<Entity>> to LiveData<List<Date>>

Question

My project is an expense tracker where I show a list of Dates under which I have a list of expenses that happened on those dates. I have nested RecyclerViews. Parent RecyclerView is a list of unique dates of all expenses. Child RecyclerView is list of expenses (viewed, of course, under unique dates). My ViewModel has a list of LiveData of ExpenseEntity. The ViewModel has to have a list of LiveData of Date which contains unique dates. I get my list of ExpenseEntity from a Room database.

My main fragments observes the LiveData of ExpenseEntities because then is when I need to update my parent and child recyclerviews.

I cannot figure out how to use Transformations.map to have a live transforming list of unique dates. How should I make sure the LiveData of Dates is always updated once LiveData of ExpenseEntity is updated?

MainActivityViewModel.kt

class MainActivityViewModel(private val expenseDao: ExpenseDao) : ViewModel() {
    val allExpenses : LiveData<List<ExpenseEntity>> = expenseDao.fetchAllExpenses().asLiveData()
    val uniqueDates : LiveData<List<Date>> = Transformations.map(allExpenses) {
        it.map { expense ->
            expense.date!!
        }.distinct()
    }
...
}

ExpensesFragment.kt

val factory = MainActivityViewModelFactory((activity?.application as SimpleExpenseTrackerApp).db.expenseDao())
expensesViewModel = ViewModelProvider(this, factory).get(MainActivityViewModel::class.java)


binding.rvParentExpenseDates.layoutManager = LinearLayoutManager(requireContext())
expensesViewModel.allExpenses.observe(viewLifecycleOwner){ expensesList ->
    if (expensesList.isNotEmpty()){
       binding.rvParentExpenseDates.adapter = expensesViewModel.uniqueDates.value?.let {
           ParentDatesAdapter(it, expensesList) { expenseId ->
               Toast.makeText(requireContext(), "Clicked expense with id: $expenseId", Toast.LENGTH_LONG).show()
                }
            }
       binding.rvParentExpenseDates.visibility = View.VISIBLE
    } else {
       binding.rvParentExpenseDates.visibility = View.GONE
    }
}

ExpenseEntity.kt

@Entity(tableName = "expense-table")
data class ExpenseEntity(
    @PrimaryKey(autoGenerate = true)
    val id: Int = 0,
    @ColumnInfo(name = "date-time")
    val dateTime : Date?,
    val date : Date?,
    @ColumnInfo(name = "account-type")
    val accountType : String = "",
    val category : String = "",
    val amount : Double = 0.0,
    val currency : String = "",
    val note : String = ""

)