argument type 'Future Function(int, String, String, String)' can't be assigned to the parameter type 'void Function(int, String?, String?, String?)?

import 'package:flutter/foundation.dart';
import 'package:flutter_local_notifications/flutter_local_notifications.dart';

class NotificationManager {
// ignore: prefer_typing_uninitialized_variables
var flutterLocalNotificationsPlugin;

NotificationManager() {
flutterLocalNotificationsPlugin = FlutterLocalNotificationsPlugin();
initNotifications();
 }

getNotificationInstance() {
return flutterLocalNotificationsPlugin;
}

void initNotifications() {
// initialise the plugin. app_icon needs to be a added as a drawable resource to the 
Android head project
const initializationSettingsAndroid =
    AndroidInitializationSettings('@mipmap/launcher_icon');
const initializationSettingsIOS = IOSInitializationSettings(

I AM GETTING AN ERROR ON THIS onDidReceiveLocalNotification
The argument type ‘Future Function(int, String, String, String)’ can’t be assigned to the parameter type ‘void Function(int, String?, String?, String?)?

  onDidReceiveLocalNotification: onDidReceiveLocalNotification);

const initializationSettings =  InitializationSettings(
    android: initializationSettingsAndroid, iOS: initializationSettingsIOS);

flutterLocalNotificationsPlugin.initialize(initializationSettings,
    onSelectNotification: onSelectNotification);
    }

void showNotificationDaily(
  int id, String title, String body, int hour, int minute) async {
var time = Time(hour, minute, 0);
await flutterLocalNotificationsPlugin.showDailyAtTime(
    id, title, body, time, getPlatformChannelSpecfics());
if (kDebugMode) {
  print('Notification Succesfully Scheduled at ${time.toString()}');
  }
 }

getPlatformChannelSpecfics() {
var androidPlatformChannelSpecifics = const AndroidNotificationDetails(
     'your channel name', 'your channel description',
    importance: Importance.max,
    priority: Priority.high,
    ticker: 'Sickle Cell');
var iOSPlatformChannelSpecifics = const IOSNotificationDetails();
var platformChannelSpecifics = NotificationDetails(
    android: androidPlatformChannelSpecifics, iOS: iOSPlatformChannelSpecifics);

 return platformChannelSpecifics;
 }

Future onSelectNotification(String payload) async {
if (kDebugMode) {
  print('Notification clicked');
  }
  return Future.value(0);
 }

 Future onDidReceiveLocalNotification(
  int id, String title, String body, String payload) async {
  return Future.value(1);
  }

 void removeReminder(int notificationId) {
 flutterLocalNotificationsPlugin.cancel(notificationId);
 }
 }

I have read the flutter_local_notifications readme but i am still not getting it.

>Solution :

The strings in onDidReceiveLocalNotification should be nullable. Try changing:

Future onDidReceiveLocalNotification(
  int id, String title, String body, String payload) async {
  return Future.value(1);
}

To:

Future onDidReceiveLocalNotification(
      int id, String? title, String? body, String? payload) async {
      return Future.value(1);
}