fix: #425

Author: asjqkkkk

packages/self_storing_input/lib/src/self_storing_checkbox/custom_checkbox.dart

@@ -41,7 +41,7 @@ class _CustomCheckboxState extends State<CustomCheckbox> {
   void _showOverlay() {
     widget.state.overlayController.close();
     _overlay = _buildOverlay(context);
-    Overlay.of(context)!.insert(_overlay!);
+    Overlay.of(context).insert(_overlay!);
   }
 
   void _closeOverlay() {

packages/self_storing_input/lib/src/self_storing_radio_group/custom_radio.dart

@@ -54,7 +54,7 @@ class CustomRadio extends StatelessWidget {
   void _showOverlay(BuildContext context) {
     state!.closeOverlay();
     state!.overlay = _buildOverlay(context);
-    Overlay.of(context)!.insert(state!.overlay!);
+    Overlay.of(context).insert(state!.overlay!);
   }
 
   OverlayEntry _buildOverlay(BuildContext context) {

packages/self_storing_input/lib/src/self_storing_text/edit_button.dart

@@ -42,7 +42,7 @@ class _EditButtonState extends State<EditButton> {
       onPressed: () {
         widget.state.overlayController.close();
         _overlay = _buildOverlay(context);
-        Overlay.of(context)!.insert(_overlay!);
+        Overlay.of(context).insert(_overlay!);
       },
     );
   }