TF-37 Generate tree with Map

lib/features/mailbox/presentation/model/mailbox_node.dart

@@ -1,4 +1,3 @@
-import 'package:built_collection/built_collection.dart';
 import 'package:equatable/equatable.dart';
 import 'package:jmap_dart_client/jmap/core/id.dart';
 import 'package:jmap_dart_client/jmap/mail/mailbox/mailbox.dart';
@@ -8,39 +7,19 @@ class MailboxNode with EquatableMixin{
   static PresentationMailbox _root = PresentationMailbox(MailboxId(Id('root')));
 
   PresentationMailbox item;
-  late BuiltList<MailboxNode> childrenItems;
+  List<MailboxNode>? childrenItems;
 
   factory MailboxNode.root() => MailboxNode(_root);
 
-  bool hasChildren() => childrenItems.isNotEmpty;
+  bool hasChildren() => childrenItems?.isNotEmpty ?? false;
 
-  MailboxNode(this.item, {List<MailboxNode> child = const []}) {
-    this.childrenItems = BuiltList(child);
-  }
+  MailboxNode(this.item, {this.childrenItems});
 
-  MailboxNode? addChild(PresentationMailbox mailbox) {
-    if (_validateChild(mailbox)) {
-      final node = MailboxNode(mailbox);
-      _addChildNode(node);
-      return node;
+  void addChildNode(MailboxNode node) {
+    if (childrenItems == null) {
+      childrenItems = [];
     }
-    return null;
-  }
-
-  void _addChildNode(MailboxNode node) {
-    childrenItems = (ListBuilder<MailboxNode>(childrenItems)
-        ..add(node))
-      .build();
-  }
-
-  bool _validateChild(PresentationMailbox mailbox) {
-    if (mailbox.parentId == item.id) {
-      return true;
-    }
-    if (item == _root) {
-      return true;
-    }
-    return false;
+    childrenItems?.add(node);
   }
 
   @override