update user model

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

@@ -8,8 +8,8 @@ part 'user.g.dart';
 class User {
   /// Constructor used for json serialization
   User({
-    this.id = '',
-    this.role = '',
+    required this.id,
+    this.role,
     DateTime? createdAt,
     DateTime? updatedAt,
     this.lastActive,
@@ -24,18 +24,6 @@ class User {
   factory User.fromJson(Map<String, dynamic> json) => _$UserFromJson(
       Serialization.moveToExtraDataFromRoot(json, topLevelFields));
 
-  /// Use this named constructor to create a new user instance
-  User.init(
-    this.id, {
-    this.online = false,
-    this.extraData = const {},
-    required this.createdAt,
-    required this.updatedAt,
-    this.teams = const [],
-    required this.role,
-  })   : lastActive = null,
-        banned = false;
-
   /// Known top level fields.
   /// Useful for [Serialization] methods.
   static const topLevelFields = [
@@ -53,9 +41,8 @@ class User {
   final String id;
 
   /// User role
-  @JsonKey(
-      includeIfNull: false, toJson: Serialization.readOnly, defaultValue: '')
-  final String role;
+  @JsonKey(includeIfNull: false, toJson: Serialization.readOnly)
+  final String? role;
 
   /// User role
   @JsonKey(