improvement: avoid save null field

lib/models/account.dart

@@ -3,7 +3,7 @@ import 'package:meta/meta.dart';
 
 part 'account.g.dart';
 
-@JsonSerializable()
+@JsonSerializable(includeIfNull: false)
 class Account {
   String platform;
   String domain;

lib/models/account.g.dart

@@ -17,11 +17,20 @@ Account _$AccountFromJson(Map<String, dynamic> json) {
   );
 }
 
-Map<String, dynamic> _$AccountToJson(Account instance) => <String, dynamic>{
-      'platform': instance.platform,
-      'domain': instance.domain,
-      'token': instance.token,
-      'login': instance.login,
-      'avatarUrl': instance.avatarUrl,
-      'gitlabId': instance.gitlabId,
-    };
+Map<String, dynamic> _$AccountToJson(Account instance) {
+  final val = <String, dynamic>{};
+
+  void writeNotNull(String key, dynamic value) {
+    if (value != null) {
+      val[key] = value;
+    }
+  }
+
+  writeNotNull('platform', instance.platform);
+  writeNotNull('domain', instance.domain);
+  writeNotNull('token', instance.token);
+  writeNotNull('login', instance.login);
+  writeNotNull('avatarUrl', instance.avatarUrl);
+  writeNotNull('gitlabId', instance.gitlabId);
+  return val;
+}

lib/models/auth.dart

@@ -58,7 +58,6 @@ class AuthModel with ChangeNotifier {
       }
     }
     newAccounts.add(account);
-
     _accounts = newAccounts;
 
     // Save