How can I fix the error in calendar_view use of my code in Flutter?

Question

I wrote the following code but I got the error in the screenshot. I added everything from pub.dev, I only wrote Event class on my own, I am also adding it here. Can you help me on solving?

I am kind of learning these topics recently so my mistake might be really simple but it would be great if you could spend some time on it.

import 'dart:ui';

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

import 'calendarFiles/model/event.dart';
import 'calendarFiles/pages/mobile/mobile_home_page.dart';
import 'calendarFiles/pages/web/web_home_page.dart';
import 'calendarFiles/widgets/responsive_widget.dart';

DateTime get _now => DateTime.now();

class CalendarScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return CalendarControllerProvider<Event>(
      controller: EventController<Event>()..addAll(_events),
      child: MaterialApp(
        title: 'Calendar',
        debugShowCheckedModeBanner: false,
        theme: ThemeData.light(),
        scrollBehavior: ScrollBehavior().copyWith(
          dragDevices: {
            PointerDeviceKind.trackpad,
            PointerDeviceKind.mouse,
            PointerDeviceKind.touch,
          },
        ),
        home: ResponsiveWidget(
          mobileWidget: MobileHomePage(),
          webWidget: WebHomePage(),
        ),
      ),
    );
  }
}

List<CalendarEventData<Event>> _events = [
  CalendarEventData(
    date: _now,
    event: Event(title: "Joe's Birthday"),
    title: "Project meeting",
    description: "Today is project meeting.",
    startTime: DateTime(_now.year, _now.month, _now.day, 18, 30),
    endTime: DateTime(_now.year, _now.month, _now.day, 22),
  ),
... more events ...
];

class EventDetailsScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Event Details'),
      ),
      body: Center(
        child: Text('Event Details Screen'),
      ),
    );
  }
}

class Event {
  final String title;
  final String description;
  final DateTime? startTime;
  final DateTime? endTime;

  Event({
    required this.title,
    this.description = '',
    this.startTime,
    this.endTime,
  });

  @override
  bool operator ==(Object other) {
    if (identical(this, other)) return true;

    return other is Event &&
        other.title == title &&
        other.description == description &&
        other.startTime == startTime &&
        other.endTime == endTime;
  }

  @override
  int get hashCode {
    return title.hashCode ^
    description.hashCode ^
    startTime.hashCode ^
    endTime.hashCode;
  }
}

I tried changing Event class but it didn't work.