Minimal Example to Reproduce Flutter Framework Assertion Error

main.dart

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

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: MyHome(),
    );
  }
}

class MyHome extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('minimal example'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'Press + to provoke the error',
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          showSearch(
              context: context,
              delegate: _TaskWithProjectSearchDelegate(
                suggestions: [
                  TaskWithProject(718, 'A', 6600, 'zFriedhof', 'zFriedhof'),
                  TaskWithProject(718, 'A', 6605, 'zFriedhof', 'zFriedhof'),
                  TaskWithProject(718, 'A', 6611, 'zFriedhof', 'zFriedhof'),
                ],
              )).then((task) {});
        },
        child: Icon(Icons.add),
      ),
    );
  }
}

class TaskWithProject extends Comparable<TaskWithProject> {
  final int projectId;
  final String projectName;
  final int id;
  final String taskList;
  final String name;

  TaskWithProject(this.projectId, this.projectName, this.id, this.taskList, this.name);

  String get _compareString => '$projectName :: $taskList :: $name';

  @override
  int compareTo(TaskWithProject other) {
    return this._compareString.compareTo(other._compareString);
  }
}

class _TaskWithProjectSearchDelegate extends SearchDelegate<TaskWithProject> {
  final List<TaskWithProject> suggestions;

  _TaskWithProjectSearchDelegate({@required this.suggestions});

  @override
  List<Widget> buildActions(BuildContext context) => <Widget>[];

  @override
  Widget buildLeading(BuildContext context) {
    return IconButton(
      icon: AnimatedIcon(
        icon: AnimatedIcons.menu_arrow,
        progress: transitionAnimation,
      ),
      onPressed: () {},
    );
  }

  @override
  Widget buildResults(BuildContext context) {
    return null;
  }

  @override
  Widget buildSuggestions(BuildContext context) {
    return ListView(
      children: this.suggestions.expand((TaskWithProject task) {
        return <Widget>[
          Text('[#${task.projectId}] ${task.projectName}'),
          Text(task.taskList),
          GestureDetector(
            key: Key('${task.name}'), // <-- this causes the error (duplicated Key)
            child: Text('[#${task.id}] ${task.name}')
          ),
        ];
      }).toList(),
    );
  }
}