fix(realtime_client): make ref field optional in Message class (#1284)

* fix(realtime_client): make ref field optional in Message class

Make the ref field nullable (String?) and optional in the Message constructor
to match JavaScript SDK behavior. This allows null refs in scenarios like
heartbeats and aligns with the JavaScript SDK implementation.

- Changed ref from String to String?
- Made ref optional in constructor
- Updated toJson() to conditionally include ref only when not null
- Added comprehensive tests for null ref scenarios

Closes SDK-531

* fix: remove unused import

Author: grdsdev

packages/realtime_client/lib/src/message.dart

@@ -5,14 +5,14 @@ class Message {
   final String topic;
   final ChannelEvents event;
   final dynamic payload;
-  final String ref;
+  final String? ref;
   final String? joinRef;
 
   Message({
     required this.topic,
     required this.event,
     required this.payload,
-    required this.ref,
+    this.ref,
     this.joinRef,
   });
 
@@ -48,7 +48,7 @@ class Message {
       'event':
           event != ChannelEvents.heartbeat ? event.eventName() : 'heartbeat',
       'payload': processedPayload,
-      'ref': ref,
+      if (ref != null) 'ref': ref,
       if (joinRef != null) 'join_ref': joinRef,
     };
   }

packages/realtime_client/test/message_test.dart

@@ -0,0 +1,94 @@
+import 'package:realtime_client/src/constants.dart';
+import 'package:realtime_client/src/message.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('Message', () {
+    test('message with null refs serializes correctly', () {
+      final message = Message(
+        topic: 'phoenix',
+        event: ChannelEvents.heartbeat,
+        payload: {},
+        ref: null,
+        joinRef: null,
+      );
+      final json = message.toJson();
+      expect(json['ref'], isNull);
+      expect(json['join_ref'], isNull);
+      expect(json['topic'], equals('phoenix'));
+      expect(json['event'], equals('heartbeat'));
+      expect(json['payload'], equals({}));
+    });
+
+    test('heartbeat message with null joinRef', () {
+      final message = Message(
+        topic: 'phoenix',
+        event: ChannelEvents.heartbeat,
+        payload: {},
+        ref: '123',
+        joinRef: null,
+      );
+      final json = message.toJson();
+      expect(json['ref'], equals('123'));
+      expect(json.containsKey('join_ref'), isFalse);
+      expect(json['topic'], equals('phoenix'));
+      expect(json['event'], equals('heartbeat'));
+    });
+
+    test('message with null ref but valid joinRef', () {
+      final message = Message(
+        topic: 'room:lobby',
+        event: ChannelEvents.join,
+        payload: {'user_id': '123'},
+        ref: null,
+        joinRef: 'join-456',
+      );
+      final json = message.toJson();
+      expect(json.containsKey('ref'), isFalse);
+      expect(json['join_ref'], equals('join-456'));
+      expect(json['topic'], equals('room:lobby'));
+      expect(json['payload'], equals({'user_id': '123'}));
+    });
+
+    test('message with both ref and joinRef', () {
+      final message = Message(
+        topic: 'room:lobby',
+        event: ChannelEvents.join,
+        payload: {'user_id': '123'},
+        ref: 'ref-789',
+        joinRef: 'join-456',
+      );
+      final json = message.toJson();
+      expect(json['ref'], equals('ref-789'));
+      expect(json['join_ref'], equals('join-456'));
+      expect(json['topic'], equals('room:lobby'));
+      expect(json['payload'], equals({'user_id': '123'}));
+    });
+
+    test('message with ref but null joinRef', () {
+      final message = Message(
+        topic: 'room:lobby',
+        event: ChannelEvents.leave,
+        payload: {},
+        ref: 'ref-999',
+        joinRef: null,
+      );
+      final json = message.toJson();
+      expect(json['ref'], equals('ref-999'));
+      expect(json.containsKey('join_ref'), isFalse);
+      expect(json['topic'], equals('room:lobby'));
+    });
+
+    test('ref parameter is optional in constructor', () {
+      final message = Message(
+        topic: 'phoenix',
+        event: ChannelEvents.heartbeat,
+        payload: {},
+        // ref is not provided, should be null
+      );
+      expect(message.ref, isNull);
+      final json = message.toJson();
+      expect(json.containsKey('ref'), isFalse);
+    });
+  });
+}