update discount

lib/pages/discount/model/discount_model.dart

@@ -14,10 +14,11 @@ class DiscountModel extends BaseModel {
   StreamSubscription<QuerySnapshot>? listener;
 
   List<Discount> _discounts = [];
-  List<Discount> get discounts =>
-      _selectedIndex == 1 ? _discounts : List<Discount>.from(_used.values);
+  List<Discount> get discounts => _selectedIndex == 1
+      ? _discounts
+      : List<Discount>.from(_used?.values ?? []);
 
-  late Paginator _used;
+  Paginator? _used;
   bool isLoading = false;
   int _selectedIndex = 1;
   set selectedIndex(int index) {
@@ -31,7 +32,7 @@ class DiscountModel extends BaseModel {
     _selectedIndex = 1;
     _load();
     if (_getUsed() != null) _used = _getUsed();
-    _used.load();
+    _used?.load();
   }
 
   void initUser(user) {
@@ -49,8 +50,7 @@ class DiscountModel extends BaseModel {
           .listen((snaps) {
         _discounts.clear();
         snaps.docs.forEach((d) {
-          _discounts
-              .add(Discount.fromMap(d.data() as Map<String, dynamic>, d.id));
+          _discounts.add(Discount.fromMap(d.data(), d.id));
         });
         notifyListeners();
       });
@@ -94,10 +94,10 @@ class DiscountModel extends BaseModel {
   }
 
   Future<void> loadMore() async {
-    if (_used.ended || _selectedIndex == 1) return;
+    if (_used!.ended || _selectedIndex == 1) return;
     isLoading = true;
     notifyListeners();
-    await _used.load(onFinished: () {
+    await _used!.load(onFinished: () {
       isLoading = false;
       notifyListeners();
     });
@@ -105,7 +105,7 @@ class DiscountModel extends BaseModel {
 
   Future<void> refresh() async {
     if (_selectedIndex == 1) return;
-    await _used.refresh(onFinished: () {
+    await _used!.refresh(onFinished: () {
       notifyListeners();
     });
   }
@@ -113,7 +113,7 @@ class DiscountModel extends BaseModel {
   @override
   logout() async {
     if (listener != null) await listener!.cancel();
-    if (_used != null) _used.close();
+    if (_used != null) _used!.close();
 
     _discounts = [];
   }