diff --git a/learning/tour-of-beam/frontend/lib/components/sdk_dropdown.dart b/learning/tour-of-beam/frontend/lib/components/sdk_dropdown.dart
index 15c8cbdea97d..bfa22578757c 100644
--- a/learning/tour-of-beam/frontend/lib/components/sdk_dropdown.dart
+++ b/learning/tour-of-beam/frontend/lib/components/sdk_dropdown.dart
@@ -23,7 +23,7 @@ import 'builders/sdks.dart';
 
 class SdkDropdown extends StatelessWidget {
   final String sdkId;
-  final ValueChanged<String?> onChanged;
+  final ValueChanged<String> onChanged;
   const SdkDropdown({
     required this.sdkId,
     required this.onChanged,
@@ -40,7 +40,11 @@ class SdkDropdown extends StatelessWidget {
         return _DropdownWrapper(
           child: DropdownButton(
             value: sdkId,
-            onChanged: onChanged,
+            onChanged: (value) {
+              if (value != null) {
+                onChanged(value);
+              }
+            },
             items: sdks
                 .map(
                   (sdk) => DropdownMenuItem(