move on with the migration

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

@@ -10,7 +10,7 @@ class Serialization {
   static const Function readOnly = readonly;
 
   /// List of users to list of userIds
-  static List<String?>? userIds(List<User>? users) =>
+  static List<String>? userIds(List<User>? users) =>
       users?.map((u) => u.id).toList();
 
   /// Takes unknown json keys and puts them in the `extra_data` key
@@ -36,7 +36,6 @@ class Serialization {
   /// the json map
   static Map<String, dynamic> moveFromExtraDataToRoot(
     Map<String, dynamic> json,
-    List<String> topLevelFields,
   ) {
     final jsonClone = Map<String, dynamic>.from(json);
     return jsonClone