diff --git a/packages/realtime_client/lib/src/message.dart b/packages/realtime_client/lib/src/message.dart
index ef4fe366..6458e4f6 100644
--- a/packages/realtime_client/lib/src/message.dart
+++ b/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,
     };
   }
diff --git a/packages/realtime_client/test/message_test.dart b/packages/realtime_client/test/message_test.dart
new file mode 100644
index 00000000..8f3ed566
--- /dev/null
+++ b/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);
+    });
+  });
+}