fix: add null catch on address book request

flutter/lib/desktop/pages/connection_page.dart

@@ -414,7 +414,7 @@ class _ConnectionPageState extends State<ConnectionPage> {
             );
           } else {
             if (model.abLoading) {
-              return Center(
+              return const Center(
                 child: CircularProgressIndicator(),
               );
             } else if (model.abError.isNotEmpty) {

flutter/lib/desktop/widgets/peer_widget.dart

@@ -266,7 +266,7 @@ class AddressBookPeerWidget extends BasePeerWidget {
           loadEvent: 'load_address_book_peers',
           offstageFunc: (Peer peer) =>
               !_hitTag(gFFI.abModel.selectedTags, peer.tags),
-          peerCardWidgetFunc: (Peer peer) => DiscoveredPeerCard(
+          peerCardWidgetFunc: (Peer peer) => AddressBookPeerCard(
             peer: peer,
           ),
           initPeers: _loadPeers(),

flutter/lib/models/ab_model.dart

@@ -28,6 +28,7 @@ class AbModel with ChangeNotifier {
     try {
       final resp =
           await http.post(Uri.parse(api), headers: await _getHeaders());
+      if (resp.body.isNotEmpty && resp.body.toLowerCase() != "null") {
         Map<String, dynamic> json = jsonDecode(resp.body);
         if (json.containsKey('error')) {
           abError = json['error'];
@@ -36,13 +37,17 @@ class AbModel with ChangeNotifier {
           tags.value = data['tags'];
           peers.value = data['peers'];
         }
+        notifyListeners();
         return resp.body;
+      } else {
+        return "";
+      }
     } catch (err) {
       abError = err.toString();
     } finally {
+      notifyListeners();
       abLoading = false;
     }
-    notifyListeners();
     return null;
   }
 
@@ -60,7 +65,6 @@ class AbModel with ChangeNotifier {
     return _ffi?.getHttpHeaders();
   }
 
-  ///
   void addId(String id) async {
     if (idContainBy(id)) {
       return;