How to convert from Map<String, dynamic> to List<String> in flutter - flutter

Question

I'm trying to make multiple select widgets and the data from firebase database
CollectionReference submission = FirebaseFirestore.instance.collection('cuti'); is data with type Map<String, dynamic> while on dataSource: must be type List<object?>
this is the full code
class multiple extends StatefulWidget {
const multiple({super.key});
#override
State<multiple> createState() => _multipleState();
}
class _multipleState extends State<multiple> {
late MultiselectController _multiselectController;
late Random random;
late List<String> _items;
CollectionReference submission = FirebaseFirestore.instance.collection('cuti');
#override
void initState() {
super.initState();
_multiselectController = MultiselectController();
_items = List.generate(10, (index) => '$submission'); // in submission Type: Map<String, dynamic>
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('List'),
),
body: MultiselectScope(
controller: _multiselectController,
dataSource: _items, // in here must be Type: List<String>
clearSelectionOnPop: true,
keepSelectedItemsBetweenUpdates: true,
// initialSelectedIndexes: [1, 3],
onSelectionChanged: (selectedIndexes, selectedItems) {},
child: Padding(
padding: EdgeInsets.all(10),
child: Column(
mainAxisAlignment: MainAxisAlignment.start,
children: [
Expanded(
child: ListView.builder(
itemCount: _items.length,
itemBuilder: (context, index) {
final controller = MultiselectScope.controllerOf(context);
final itemSelected = controller.isSelected(index);
return InkWell(
onLongPress: () {
if (!controller.selectionAttached) {
controller.select(index);
}
},
onTap: () {
print('item is selected $itemSelected');
if (controller.selectionAttached) {
controller.select(index);
}
},
child: Padding(
padding: EdgeInsets.all(10),
child: Container(
color: itemSelected
? Theme.of(context).primaryColor
: null,
child: Text(
_items[index],
style: TextStyle(fontSize: 20),
),
),
),
);
},
),
)
],
),
),
),
);
}
}