fix reaction extradata

packages/stream_chat/lib/src/models/reaction.dart

@@ -15,7 +15,7 @@ class Reaction {
     this.user,
     String? userId,
     this.score = 0,
-    this.extraData,
+    this.extraData = const {},
   })  : userId = userId ?? user?.id,
         createdAt = createdAt ?? DateTime.now();
 
@@ -49,8 +49,11 @@ class Reaction {
   final String? userId;
 
   /// Reaction custom extraData
-  @JsonKey(includeIfNull: false)
+  @JsonKey(
-  final Map<String, Object?>? extraData;
+    includeIfNull: false,
+    defaultValue: {},
+  )
+  final Map<String, Object?> extraData;
 
   /// Map of custom user extraData
   static const topLevelFields = [

packages/stream_chat/lib/src/models/reaction.g.dart

@@ -18,7 +18,7 @@ Reaction _$ReactionFromJson(Map<String, dynamic> json) {
         : User.fromJson(json['user'] as Map<String, dynamic>),
     userId: json['user_id'] as String?,
     score: json['score'] as int? ?? 0,
-    extraData: json['extra_data'] as Map<String, dynamic>?,
+    extraData: json['extra_data'] as Map<String, dynamic>? ?? {},
   );
 }
 
@@ -38,6 +38,6 @@ Map<String, dynamic> _$ReactionToJson(Reaction instance) {
   writeNotNull('user', readonly(instance.user));
   val['score'] = instance.score;
   writeNotNull('user_id', readonly(instance.userId));
-  writeNotNull('extra_data', instance.extraData);
+  val['extra_data'] = instance.extraData;
   return val;
 }