I can't assign ArrayList I pulled from Flutter FirebaseFirestore to variable

Question

I have a code like this:

Array yapilacaklar;

FirebaseFirestore.instance.collection("users").doc(uID).get().then((DocumentSnapshot documentSnapshot) {
  if (documentSnapshot.exists) {
    setState(() {
      print("in InitState: " + "${documentSnapshot["yapilacaklar"]}");
      yapilacaklar = documentSnapshot["yapilacaklar"];
    });
  } else {
    setState(() {
      yapilacaklar = null;
    });
  }
});

My goal here is to pull an ArrayList from the Firestore and assign it to the ArrayList yapilacaklar's in the application, which I created as a variable. But I couldn't do it and I couldn't assign it. Is there something wrong with my code?

Full codes:

class _appState extends State<app> {
  @override
  void initState() {
    super.initState();
    var uID = FirebaseAuth.instance.currentUser.uid;
    FirebaseFirestore.instance.collection("users").doc(uID).get().then((DocumentSnapshot documentSnapshot) {
      if (documentSnapshot.exists) {
        setState(() {
          print("in InitState: " + "${documentSnapshot["yapilacaklar"]}");
          yapilacaklar = documentSnapshot["yapilacaklar"];
        });
      } else {
        setState(() {
          yapilacaklar = null;
        });
      }
    });
    print("Yapilacaklar: " + yapilacaklar.toString());
    @override
    Widget build(BuildContext context) {
      throw UnimplementedError();
    }
  }

Console output:

Reload already in progress, ignoring request
Restarted application in 1.031ms.
I/flutter ( 7369): Yapilacaklar: null
W/DynamiteModule( 7369): Local module descriptor class for com.google.android.gms.providerinstaller.dynamite not found.
I/DynamiteModule( 7369): Considering local module com.google.android.gms.providerinstaller.dynamite:0 and remote module com.google.android.gms.providerinstaller.dynamite:0
W/ProviderInstaller( 7369): Failed to load providerinstaller module: No acceptable module com.google.android.gms.providerinstaller.dynamite found. Local version is 0 and remote version is 0.
W/ProviderInstaller( 7369): Failed to report request stats: com.google.android.gms.common.security.ProviderInstallerImpl.reportRequestStats [class android.content.Context, long, long]
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->getObject(Ljava/lang/Object;J)Ljava/lang/Object; (greylist, linking, allowed)
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putObject(Ljava/lang/Object;JLjava/lang/Object;)V (greylist, linking, allowed)
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->getInt(Ljava/lang/Object;J)I (greylist, linking, allowed)
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putInt(Ljava/lang/Object;JI)V (greylist, linking, allowed)
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putObject(Ljava/lang/Object;JLjava/lang/Object;)V (greylist, linking, allowed)
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putObject(Ljava/lang/Object;JLjava/lang/Object;)V (greylist, linking, allowed)
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putLong(Ljava/lang/Object;JJ)V (greylist, linking, allowed)
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putObject(Ljava/lang/Object;JLjava/lang/Object;)V (greylist, linking, allowed)
I/chatty  ( 7369): uid=10146(io.simto.todolist.app) FirestoreWorker identical 1 line
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putObject(Ljava/lang/Object;JLjava/lang/Object;)V (greylist, linking, allowed)
I/flutter ( 7369): in InitState: [Görev 1, Görev 2]
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putObject(Ljava/lang/Object;JLjava/lang/Object;)V (greylist, linking, allowed)
E/flutter ( 7369): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: type 'List<dynamic>' is not a subtype of type 'Array<NativeType>'
E/flutter ( 7369): #0      _appState.initState.<anonymous closure>.<anonymous closure>
E/flutter ( 7369): #1      State.setState
E/flutter ( 7369): #2      _appState.initState.<anonymous closure>
E/flutter ( 7369): #3      _rootRunUnary (dart:async/zone.dart:1434:47)
E/flutter ( 7369): #4      _CustomZone.runUnary (dart:async/zone.dart:1335:19)
E/flutter ( 7369): <asynchronous suspension>
E/flutter ( 7369):
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->getObject(Ljava/lang/Object;J)Ljava/lang/Object; (greylist, linking, allowed)
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putObject(Ljava/lang/Object;JLjava/lang/Object;)V (greylist, linking, allowed)
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->getInt(Ljava/lang/Object;J)I (greylist, linking, allowed)
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putInt(Ljava/lang/Object;JI)V (greylist, linking, allowed)
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putObject(Ljava/lang/Object;JLjava/lang/Object;)V (greylist, linking, allowed)
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putInt(Ljava/lang/Object;JI)V (greylist, linking, allowed)
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putObject(Ljava/lang/Object;JLjava/lang/Object;)V (greylist, linking, allowed)
I/chatty  ( 7369): uid=10146(io.simto.todolist.app) FirestoreWorker identical 1 line
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putObject(Ljava/lang/Object;JLjava/lang/Object;)V (greylist, linking, allowed)
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putObject(Ljava/lang/Object;JLjava/lang/Object;)V (greylist, linking, allowed)
W/to.todolist.ap( 7369): Accessing hidden method Lsun/misc/Unsafe;->putObject(Ljava/lang/Object;JLjava/lang/Object;)V (greylist, linking, allowed)

Thank you in advance for your help.