fix handling empty sessions

app/lib/features/settings/data/repositories/settings_repository.dart

@@ -29,7 +29,9 @@ class SettingsRepository extends _$SettingsRepository {
       if (oldSettings.kagiSession != newSettings.kagiSession) {
         await _flutterSecureStorage.write(
           key: _sessionStorageKey,
-          value: newSettings.kagiSession,
+          value: (newSettings.kagiSession?.isNotEmpty ?? false)
+              ? newSettings.kagiSession
+              : null,
         );
       }
 

app/lib/main.dart

@@ -48,9 +48,11 @@ void main() async {
               }
 
               if (settings.kagiSession case final String session) {
-                await ref
-                    .read(sessionServiceProvider.notifier)
-                    .setKagiSession(session);
+                if (session.isNotEmpty) {
+                  await ref
+                      .read(sessionServiceProvider.notifier)
+                      .setKagiSession(session);
+                }
               }
 
               ref.read(sessionServiceProvider.notifier).initializationDone();