flutter_graphql不起作用，在应用构建后总是返回null

import 'package:flutter/material.dart';
import 'package:graphql_flutter/graphql_flutter.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return GraphQLProvider(
      client: ValueNotifier(GraphQLClient(
        link: HttpLink('https://your-graphql-endpoint.com/graphql'),
        cache: InMemoryCache(),
      )),
      child: MaterialApp(
        home: Query(
          options: QueryOptions(
            document: gql(r'''
              query GetUsers {
                users {
                  id
                  name
                }
              }
            '''),
          ),
          builder: (QueryResult result, {VoidCallback refetch, FetchMore fetchMore}) {
            if (result.hasException) {
              return Text(result.exception.toString());
            }

            if (result.isLoading) {
              return CircularProgressIndicator();
            }

            return ListView.builder(
              itemCount: result.data['users'].length,
              itemBuilder: (context, index) {
                var user = result.data['users'][index];
                return ListTile(
                  title: Text(user['name']),
                );
              },
            );
          },
        ),
      ),
    );
  }
}