[Flutter] How to solve the "type 'null' is not a subtype of type object" error

I want to make a set profile page that when user must upload the profile picture, and if the upload image success it will make the auth success and redirect to homepage.But, when I run the code below, it shows the error that says "type 'null' is not a subtype of type object"

this is my model class for the Sign Up Form

class SignUpFormModel {
final String? name;
final String? email;
final String? password;
final String? profilePicture;

SignUpFormModel({
this.name,
this.email,
this.password,
this.profilePicture,
});

Map<String, dynamic> toJson() {
return {
'name': name,
'email': email,
'username': password,
'profile_picture': profilePicture,
};
}

SignUpFormModel copyWith({
String? profilePicture,
}) =>
SignUpFormModel(
name: name,
email: email,
password: password,
profilePicture: profilePicture ?? this.profilePicture,
);
}



And this is my set profile page

import 'dart:convert';
import 'dart:io';

import 'package:another_flushbar/flushbar.dart';
import 'package:baca_app/blocs/auth/auth_bloc.dart';
import 'package:baca_app/models/sign_up_form_model.dart';
import 'package:baca_app/shared/shared_methods.dart';
import 'package:baca_app/shared/theme.dart';
import 'package:baca_app/ui/pages/sign_up_success_page.dart';
import 'package:baca_app/ui/widgets/buttons.dart';
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:image_picker/image_picker.dart';

class SignUpSetProfilePage extends StatefulWidget {
final SignUpFormModel data;

const SignUpSetProfilePage({
super.key,
required this.data,
});

@override
State<SignUpSetProfilePage> createState() => _SignUpSetProfilePageState();
}

class _SignUpSetProfilePageState extends State<SignUpSetProfilePage> {
XFile? selectedImage;

selectImage() async {
final imagePicker = ImagePicker();
final XFile? image =
await imagePicker.pickImage(source: ImageSource.gallery);

if (image != null) {
setState(() {
selectedImage = image;
});
}
}

@override
Widget build(BuildContext context) {
return Scaffold(
body: BlocConsumer<AuthBloc, AuthState>(
listener: (context, state) {
if (state is AuthFailed) {
showCustomSnackbar(context, state.e);
}
if (state is AuthSuccess) {
Navigator.pushNamedAndRemoveUntil(
context, '/home', (route) => false);
}
},
builder: (context, state) {
if (state is AuthLoading) {
return const Center(
child: CircularProgressIndicator(),
);
}
return ListView(
padding: const EdgeInsets.symmetric(
horizontal: 24,
),
children: [
Container(
padding: const EdgeInsets.all(22),
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(20),
color: whiteColor,
),
child: Column(
children: [
const SizedBox(
height: 50,
),
Text(
'Daftar',
style: opensansGreyTextStyle.copyWith(
fontSize: 24,
fontWeight: bold,
),
),
const SizedBox(
height: 8,
),
Text(
'Masukin foto profil yuk',
style: robotoSoftGreyTextStyle.copyWith(
fontSize: 16,
fontWeight: regular,
),
),
const SizedBox(
height: 24,
),
GestureDetector(
onTap: () {
selectImage();
},
child: Container(
width: 120,
height: 120,
decoration: BoxDecoration(
shape: BoxShape.circle,
color: lightBackgroundColor,
image: selectedImage == null
? null
: DecorationImage(
fit: BoxFit.cover,
image: FileImage(
File(
selectedImage!.path,
),
),
),
),
child: selectedImage != null
? null
: Center(
child: Image.asset(
'assets/ic_upload.png',
width: 32,
),
),
),
),
const SizedBox(
height: 16,
),
Text(
'Shayna Hanna',
style: opensansGreyTextStyle.copyWith(
fontSize: 18,
fontWeight: medium,
),
),
const SizedBox(
height: 30,
),
CustomFilledButton(
title: 'Continue',
onPressed: () {
if (selectedImage == null) {
ScaffoldMessenger.of(context).showSnackBar(
SnackBar(
content: const Text(
'Gambar tidak boleh kosong',
),
backgroundColor: redColor,
),
);
} else {
context.read<AuthBloc>().add(
AuthRegister(
widget.data.copyWith(
profilePicture:
'data:image/png;base64,${base64Encode(File(selectedImage!.path).readAsBytesSync())}',
),
),
);
}
}),
],
),
),
const SizedBox(
height: 50,
),
],
);
},
),
);
}
}



I make my profilePicture fields optional but i don't understand why this error show up

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