How can I retrieve 3 collections from Firestore in a FutureBuilder? Using Future.wait but getting errors

I need to pull three lists from Firestore before building my UI. Using a Future.wait I am getting an error. Here is my code:

Here is the declaration of the variables for the futures:

 // Variables for the futures Future<List<FilingData>>? filingList; Future<List<ClientData>>? clientList; Future<List<UserData>>? userList; // Variables for the retrieved data List<FilingData>? retrievedFilingList; List<ClientData>? retrievedClientList; List<UserData>? retrievedUserList; 

Here is the function that pulls the first list (the other two are just like it):

Future<List<FilingData>> retrieveFilings() async { QuerySnapshot<Map<String, dynamic>> snapshot = await _db.collection('filings').get(); return snapshot.docs .map((docSnapshot) => FilingData.fromDocumentSnapshot(docSnapshot)) .toList(); } 

Here is the initialization of the futures:

@override void initState() { super.initState(); _initRetrieval(); // obtain the futures here. Must be done here to avoid creating every build. } // Set up the futures for the FutureBuilder and the data lists upon retrieval. Future<void> _initRetrieval() async { filingList = filingService.retrieveFilings(); retrievedFilingList = await filingService.retrieveFilings(); clientList = clientService.retrieveClients(); retrievedClientList = await clientService.retrieveClients(); userList = userService.retrieveUsers(); retrievedUserList = await userService.retrieveUsers(); } 

Here is the FutureBuilder:

 @override Widget build(BuildContext context) { return FutureBuilder( future: Future.wait([filingList, clientList, userList]), builder: (context, AsyncSnapshot<List<dynamic>> snapshot) { if (snapshot.hasData && snapshot.data!.isNotEmpty) { return Material( <Build UI> ... 

And here is the lint error which is on [filingList, clientList, userList] in the Future.wait:

Couldn't infer type parameter 'E'. Tried to infer 'Future<List<Object>>?' for 'E' which doesn't work: Return type declared as 'List<E>'used where 'Iterable<Future<_>>' is required. The type 'Future<List<Object>>?' was inferred from: Parameter 'element' declared as 'E' but argument is 'Future<List<FilingData>>?'. Parameter 'element' declared as 'E' but argument is 'Future<List<ClientData>>?'. Parameter 'element' declared as 'E' but argument is 'Future<List<UserData>>?'. 

So I added <List<dynamic>> to the Future.wait like this:

future: Future.wait<List<dynamic>>([filingList, clientList, userList]) 

and now I'm getting other type errors:

The element type 'Future<List<FilingData>>?' can't be assigned to the list type 'Future<List<dynamic>>'. 

This seems like a common problem, which I tried to fix with late Future<List<FilingData>> filingList; in the declarations. But it crashes on the late as not initialized.