Exception caught by gesture 'then' was called on null - flutter

Question

I faced this error when I tried to insert image
"The following NoSuchMethodError was thrown while handling a gesture:
The method 'then' was called on null.
Receiver: null
Tried calling: then(Closure: (dynamic) => Null)"
Below is my code. Hope someone can help me with it. I have no idea how to solve it. Thank you.
// ignore_for_file: import_of_legacy_library_into_null_safe, unrelated_type_equality_checks
import 'dart:io';
import 'package:dparking/model/user_model.dart';
import 'package:dparking/screens/home_screen.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:fluttertoast/fluttertoast.dart';
import 'package:image_picker/image_picker.dart';
class RegistrationScreen extends StatefulWidget {
const RegistrationScreen({Key? key}) : super(key: key);
#override
State<RegistrationScreen> createState() => _RegistrationScreenState();
}
class _RegistrationScreenState extends State<RegistrationScreen> {
final _auth = FirebaseAuth.instance;
// form key
final _formKey = GlobalKey<FormState>();
// editing Controller
final nameEditingController = TextEditingController();
final emailEditingController = TextEditingController();
final passwordEditingController = TextEditingController();
final confirmPasswordEditingController = TextEditingController();
final phoneNumberEditingController = TextEditingController();
XFile? _logo;
final ImagePicker _picker = ImagePicker();
#override
Widget build(BuildContext context) {
// Name field
final nameField = TextFormField(
autofocus: false,
controller: nameEditingController,
keyboardType: TextInputType.emailAddress,
validator: (value) {
RegExp regex = RegExp(r'^.{3,}$');
if(value!.isEmpty){
return ("Name cannot be Empty");
}
if(!regex.hasMatch(value))
{
return ("Enter Valid Name(Min. 3 Character");
}
return null;
},
onSaved: (value)
{
nameEditingController.text = value!;
},
textInputAction: TextInputAction.next,
decoration: InputDecoration(
prefixIcon: const Icon(Icons.account_circle),
contentPadding: const EdgeInsets.fromLTRB(20, 15, 20, 15),
hintText: "Name",
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(10),
),
),
);
// Email field
final emailField = TextFormField(
autofocus: false,
controller: emailEditingController,
keyboardType: TextInputType.emailAddress,
validator: (value)
{
if(value!.isEmpty)
{
return ("Please Enter Your Email");
}
// reg expression for email validation
if(!RegExp("^[a-zA-Z0-9+_.-]+#[a-zA-Z0-9.-]+.[a-z]").hasMatch(value))
{
return("Please Enter a valid email");
}
return null;
},
onSaved: (value)
{
emailEditingController.text = value!;
},
textInputAction: TextInputAction.next,
decoration: InputDecoration(
prefixIcon: const Icon(Icons.mail),
contentPadding: const EdgeInsets.fromLTRB(20, 15, 20, 15),
hintText: "Email",
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(10),
),
),
);
// Password field
final passwordField = TextFormField(
autofocus: false,
controller: passwordEditingController,
obscureText: true,
validator: (value) {
RegExp regex = RegExp(r'^.{6,}$');
if(value!.isEmpty){
return ("Password is required for login");
}
if(!regex.hasMatch(value))
{
return ("Enter Valid Password(Min. 6 Character");
}
return null;
},
onSaved: (value)
{
passwordEditingController.text = value!;
},
textInputAction: TextInputAction.next,
decoration: InputDecoration(
prefixIcon: const Icon(Icons.vpn_key),
contentPadding: const EdgeInsets.fromLTRB(20, 15, 20, 15),
hintText: "Password",
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(10),
),
),
);
// Confirm Password field
final confirmPasswordField = TextFormField(
autofocus: false,
controller: confirmPasswordEditingController,
obscureText: true,
validator: (value)
{
if(confirmPasswordEditingController.text.length !=
passwordEditingController.text){
return "Password Does Not Match";
}
return null;
},
onSaved: (value)
{
confirmPasswordEditingController.text = value!;
},
textInputAction: TextInputAction.next,
decoration: InputDecoration(
prefixIcon: const Icon(Icons.vpn_key),
contentPadding: const EdgeInsets.fromLTRB(20, 15, 20, 15),
hintText: "Confirm Password",
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(10),
),
),
);
//signup button
final signupButton = Material(
elevation: 5,
borderRadius: BorderRadius.circular(30),
color: Colors.redAccent,
child: MaterialButton(
padding: const EdgeInsets.fromLTRB(20, 15, 20, 15),
minWidth: MediaQuery.of(context).size.width,
onPressed: () {
signUp(emailEditingController.text, passwordEditingController.text);
},
child: const Text("SignUp", textAlign: TextAlign.center,
style: TextStyle(fontSize: 20, color: Colors.white, fontWeight: FontWeight.bold,),
),
),
);
return Scaffold(
backgroundColor: Colors.white,
appBar: AppBar(
backgroundColor: Colors.transparent,
elevation: 0,
leading: IconButton(
icon: const Icon(Icons.arrow_back, color: Colors.red),
onPressed: (){
Navigator.of(context).pop();
},
),
),
body: Center(
child: SingleChildScrollView(
child: Container(
color: Colors.white,
child: Padding(
padding: const EdgeInsets.all(36.0),
child: Form(
key: _formKey,
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
SizedBox(
height: 200,
width: 300,
child: Image.asset("assets/images/DParking.png",
fit: BoxFit.contain,
color: Colors.black,
),
),
nameField,
const SizedBox(height: 30),
emailField,
const SizedBox(height: 30),
passwordField,
const SizedBox(height: 30),
confirmPasswordField,
const SizedBox(height: 30),
InkWell(
onTap: (){
_pickImage().then((value){ //i think the error is here
setState((){
_logo = value;
});
});
},
child: Card(
elevation: 4,
child: _logo==null ? const SizedBox(
height: 100,
width: 250,
child: Center(
child: Text('Insert Identification Card'),
),
):SizedBox(
height: 100,
width: 250,
child: Image.file(File(_logo!.path),)
),
),
),
const SizedBox(height: 30),
signupButton,
const SizedBox(height: 30),
],
),
),
),
),
),
)
);
}
void signUp(String email, String password) async
{
if (_formKey.currentState!.validate()) {
await _auth
.createUserWithEmailAndPassword(email: email, password: password)
.then((value) => {postDetailsToFirestore()})
.catchError((e) {
Fluttertoast.showToast(msg: e!.message);
});
}
}
postDetailsToFirestore() async {
// call firestore
//call user model
//send value
FirebaseFirestore firebaseFirestore = FirebaseFirestore.instance;
User? user = _auth.currentUser;
UserModel userModel = UserModel();
userModel.email = user!.email;
userModel.uid = user.uid;
userModel.name = nameEditingController.text;
await firebaseFirestore
.collection("users")
.doc(user.uid)
.set(userModel.toMap());
Fluttertoast.showToast(msg: "Account created successfully");
Navigator.pushAndRemoveUntil(
(context),
MaterialPageRoute(builder: (context) => const HomeScreen()),
(route) => false);
}
}
_pickImage() {
}