I am trying to create a to-do list app in flutter. I am facing the issue with a widget that helps me to edit an already created todo widget with respect to the title or description.

This is the pic of my todo list HomePage

This pic of my edit button

I am facing an issue after I press the save button in this widget

This is the error that I am getting

════════ Exception caught by gesture ═══════════════════════════════════════════
The following _CastError was thrown while handling a gesture:
Null check operator used on a null value
When the exception was thrown, this was the stack
#0      _EditTodoPageState.saveTodo
package:todolist/Edit_Todo_Page.dart:47
#1      _InkResponseState._handleTap
package:flutter/…/material/ink_well.dart:989
#2      GestureRecognizer.invokeCallback
package:flutter/…/gestures/recognizer.dart:198
#3      TapGestureRecognizer.handleTapUp
package:flutter/…/gestures/tap.dart:608
#4      BaseTapGestureRecognizer._checkUp
package:flutter/…/gestures/tap.dart:296
#5      BaseTapGestureRecognizer.handlePrimaryPointer
package:flutter/…/gestures/tap.dart:230
#6      PrimaryPointerGestureRecognizer.handleEvent
package:flutter/…/gestures/recognizer.dart:563
#7      PointerRouter._dispatch
package:flutter/…/gestures/pointer_router.dart:94
#8      PointerRouter._dispatchEventToRoutes.<anonymous closure>
package:flutter/…/gestures/pointer_router.dart:139
    (elided 3 frames from dart:async)
Handler: "onTap"
Recognizer: TapGestureRecognizer#25bd2
    debugOwner: GestureDetector
    state: possible
    won arena
    finalPosition: Offset(189.1, 309.1)
    finalLocalPosition: Offset(67.7, 11.1)
    button: 1
    sent tap down
════════════════════════════════════════════════════════════════════════════════

This is my edit todo widget

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:todolist/todo.dart';
import './todos.dart';
import './todo_form_widget.dart';

class EditTodoPage extends StatefulWidget {
  final Todo todo;
  const EditTodoPage({Key? key, required this.todo}) : super(key: key);

  @override
  State<EditTodoPage> createState() => _EditTodoPageState();
}

class _EditTodoPageState extends State<EditTodoPage> {
  final _formKey = GlobalKey<FormState>();
  late String title;
  late String description;
  @override
  void initState() {
    super.initState();
    title = widget.todo.title;
    description = widget.todo.description;
  }

  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("Edit Todo"),
        ),
        body: Padding(
          padding: EdgeInsets.all(16),
          child: Form(
            child: TodoFormWidget(
              title: title,
              description: description,
              onChangedTitle: (title) => setState(() => this.title = title),
              onChangedDescription: (description) =>
                  setState(() => this.description = description),
              onSavedTodo: saveTodo,
            ),
          ),
        ));
  }

  saveTodo() {
    final isValid = _formKey.currentState!.validate();
    if (!isValid) {
      return;
    } else {
      final provider = Provider.of<TodosProvider>(context, listen: false);
      provider.updateTodo(widget.todo, title, description);
      Navigator.of(context).pop();
    }
  }
}

I am getting an error in the "saveTodo()" method. I am not able to solve this error.

This is my Provider widget

import 'package:flutter/cupertino.dart';
import 'package:todolist/todo.dart';
import 'package:provider/provider.dart';

class TodosProvider extends ChangeNotifier {
  List<Todo> _todos = [
    Todo(
      createdTime: DateTime.now(),
      title: "Wake up at 6:00 AM in the morning