fix: idtyIndex is nullable

lib/providers/substrate_sdk.dart

@@ -169,7 +169,7 @@ class SubstrateSdk with ChangeNotifier {
     final idtyIndexFrom = await _getIdentityIndexOf(from);
     final idtyIndexTo = await _getIdentityIndexOf(to);
 
-    if (idtyIndexFrom == 0 || idtyIndexTo == 0) return 0;
+    if (idtyIndexFrom == null || idtyIndexTo == null) return 0;
 
     final List certData =
         await _getStorage('cert.certsByReceiver($idtyIndexTo)') ?? [];
@@ -362,7 +362,7 @@ class SubstrateSdk with ChangeNotifier {
     //     Provider.of<WalletOptionsProvider>(homeContext, listen: false);
 
     var idtyIndex = await _getIdentityIndexOf(address);
-    if (idtyIndex == 0) return [];
+    if (idtyIndex == null) return [];
 
     final Map? idtyData = await _getStorage('identity.identities($idtyIndex)');
     if (idtyData == null || idtyData['oldOwnerKey'] == null) return [];

lib/screens/wallet_view.dart

@@ -194,7 +194,7 @@ class WalletViewScreen extends StatelessWidget {
                       }
                     }
 
-                    final toStatus = snapshot.data!['toStatus'] ?? 0;
+                    final toStatus = snapshot.data!['toStatus'];
 
                     return Visibility(
                       visible: (snapshot.data != {}),
@@ -272,7 +272,7 @@ class WalletViewScreen extends StatelessWidget {
                             ),
                             const SizedBox(height: 9),
                             Text(
-                              toStatus == 0
+                              toStatus == null
                                   ? "certify".tr()
                                   : "createIdentity".tr(),
                               textAlign: TextAlign.center,