Fixes broken getAccount() on device auth

lib/src/nakama_client/nakama_api_client.dart

@@ -131,6 +131,7 @@ class NakamaRestApiClient extends NakamaBaseClient {
     final res = await _api.nakamaAuthenticateDevice(
       body: ApiAccountDevice(
         id: deviceId,
+        vars: {'foo': 'bar'},
       ),
       create: create,
       username: username,
@@ -300,7 +301,14 @@ class NakamaRestApiClient extends NakamaBaseClient {
     final res = await _api.nakamaGetAccount();
 
     final acc = Account();
-    acc.mergeFromProto3Json(res.body!.toJson());
+    // Some workaround here while protobuf expects the vars map to not be null
+    acc.mergeFromProto3Json((res.body!.copyWith(
+      devices: res.body!.devices!
+          .map((e) => e.copyWith(
+                vars: e.vars ?? {},
+              ))
+          .toList(),
+    )).toJson());
 
     return acc;
   }

test/rest/account_test.dart

@@ -0,0 +1,29 @@
+import 'package:faker/faker.dart';
+import 'package:nakama/api/api.pb.dart' as api;
+import 'package:nakama/nakama.dart';
+import 'package:nakama/src/nakama_client/nakama_api_client.dart';
+import 'package:test/scaffolding.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('[REST] Test Account', () {
+    late final NakamaBaseClient client;
+    late final Session session;
+
+    setUpAll(() async {
+      client = NakamaRestApiClient.init(
+        host: '127.0.0.1',
+        ssl: false,
+        serverKey: 'defaultkey',
+      );
+
+      session = await client.authenticateDevice(deviceId: faker.guid.guid());
+    });
+
+    test('fetching my account', () async {
+      final account = await client.getAccount(session);
+
+      expect(account, isA<api.Account>());
+    });
+  });
+}