How to describe a self closing optional element? about dart-xml-serializable HOT 3 CLOSED

import 'package:xml/xml.dart';
import 'package:xml_annotation/xml_annotation.dart' as annotation;

part 'example.g.dart';

@annotation.XmlRootElement(
  name: 'resourcetype',
  isSelfClosing: false,
)
@annotation.XmlSerializable()
class ResourceType {
  @annotation.XmlElement(
    name: 'collection',
    isSelfClosing: true,
    includeIfNull: true,
  )
  List<String?>? collection;

  ResourceType({
    this.collection,
  });

  factory ResourceType.fromXmlElement(XmlElement element) =>
      _$ResourceTypeFromXmlElement(element);

  void buildXmlChildren(
    XmlBuilder builder, {
    Map<String, String> namespaces = const {},
  }) =>
      _$ResourceTypeBuildXmlChildren(
        this,
        builder,
        namespaces: namespaces,
      );

  void buildXmlElement(
    XmlBuilder builder, {
    Map<String, String> namespaces = const {},
  }) =>
      _$ResourceTypeBuildXmlElement(
        this,
        builder,
        namespaces: namespaces,
      );

  List<XmlAttribute> toXmlAttributes({
    Map<String, String?> namespaces = const {},
  }) =>
      _$ResourceTypeToXmlAttributes(
        this,
        namespaces: namespaces,
      );

  List<XmlNode> toXmlChildren({
    Map<String, String?> namespaces = const {},
  }) =>
      _$ResourceTypeToXmlChildren(
        this,
        namespaces: namespaces,
      );

  XmlElement toXmlElement({
    Map<String, String?> namespaces = const {},
  }) =>
      _$ResourceTypeToXmlElement(
        this,
        namespaces: namespaces,
      );
}

void main(List<String> arguments) {
  var collection = ResourceType.fromXmlElement(
    XmlDocument.parse(
      '<resourcetype></resourcetype>',
    ).rootElement,
  ).collection;

  assert(collection == null);

  collection = ResourceType.fromXmlElement(
    XmlDocument.parse(
      '<resourcetype><collection/></resourcetype>',
    ).rootElement,
  ).collection;

  assert(collection != null);
}