diff --git a/lib/iap/purchase_manager.dart b/lib/iap/purchase_manager.dart
index 482b32ab..f7823c75 100644
--- a/lib/iap/purchase_manager.dart
+++ b/lib/iap/purchase_manager.dart
@@ -128,8 +128,8 @@ class PurchaseManager {
     // FIXME: What if the sotre cannot be reached?
     var response = await _instance!.con.queryProductDetails(skus);
     response.productDetails.sort((a, b) {
-      var pa = PaymentInfo.fromProductDetail(a)!;
-      var pb = PaymentInfo.fromProductDetail(b)!;
+      var pa = PaymentInfo.fromProductDetail(a);
+      var pb = PaymentInfo.fromProductDetail(b);
       return pa.value.compareTo(pb.value);
     });
 
diff --git a/lib/iap/purchase_slider.dart b/lib/iap/purchase_slider.dart
index 949daf48..b90b08d4 100644
--- a/lib/iap/purchase_slider.dart
+++ b/lib/iap/purchase_slider.dart
@@ -15,7 +15,7 @@ class PaymentInfo extends Equatable {
   @override
   List<Object> get props => [value, text, id];
 
-  static PaymentInfo? fromProductDetail(ProductDetails pd) {
+  static PaymentInfo fromProductDetail(ProductDetails pd) {
     double value = -1;
     if (pd.skProduct != null) {
       value = double.parse(pd.skProduct!.price);
@@ -34,8 +34,8 @@ class PaymentInfo extends Equatable {
 typedef PaymentSliderChanged = void Function(PaymentInfo);
 
 class PurchaseSlider extends StatelessWidget {
-  final List<PaymentInfo?> values;
-  final PaymentInfo? selectedValue;
+  final List<PaymentInfo> values;
+  final PaymentInfo selectedValue;
   final PaymentSliderChanged onChanged;
 
   PurchaseSlider({
@@ -43,7 +43,7 @@ class PurchaseSlider extends StatelessWidget {
     required this.selectedValue,
     required this.onChanged,
   }) {
-    values.sort((a, b) => a!.value.compareTo(b!.value));
+    values.sort((a, b) => a.value.compareTo(b.value));
   }
 
   @override
@@ -63,8 +63,8 @@ class PurchaseSlider extends StatelessWidget {
 }
 
 class ShapePainter extends CustomPainter {
-  final List<PaymentInfo?> values;
-  final PaymentInfo? selectedValue;
+  final List<PaymentInfo> values;
+  final PaymentInfo selectedValue;
   final Color color;
 
   ShapePainter({
@@ -91,8 +91,8 @@ class ShapePainter extends CustomPainter {
       ..strokeCap = StrokeCap.round
       ..style = PaintingStyle.fill;
 
-    var diff = (values.last!.value - values.first!.value);
-    var w = (size.width / diff) * (selectedValue!.value - values.first!.value);
+    var diff = (values.last.value - values.first.value);
+    var w = (size.width / diff) * (selectedValue.value - values.first.value);
 
     var angle = atan(size.height / size.width);
     var h = w * tan(angle);
diff --git a/lib/iap/purchase_widget.dart b/lib/iap/purchase_widget.dart
index 19156eff..a8121788 100644
--- a/lib/iap/purchase_widget.dart
+++ b/lib/iap/purchase_widget.dart
@@ -185,6 +185,10 @@ class _PurchaseWidgetState extends State<PurchaseWidget> {
   }
 
   Widget buildBody(BuildContext context) {
+    if (_products == null || _products!.isEmpty) {
+      return const Icon(Icons.error, size: 64);
+    }
+
     var slider = PurchaseSlider(
       values: _products!.map(PaymentInfo.fromProductDetail).toList(),
       selectedValue: PaymentInfo.fromProductDetail(_selectedProduct!),