Flutter Google Sign In - Email information is not coming to Firebase (returns blank)

When I log in with google in the application I made on Flutter, the email returns to firebase as a null value. I do not get any errors in the runtime or login. I made changes to the google_sign_in version on the pubspec.yaml file, but the result has not changed.

user_repository.dart :

    import 'package:pisipisikolog/locator.dart';
    import 'package:pisipisikolog/model/user_model.dart';
    import 'package:pisipisikolog/services/auth_base.dart';
    import 'package:pisipisikolog/services/fake_auth_service.dart';
    import 'package:pisipisikolog/services/firebase_auth_service.dart';
    import 'package:pisipisikolog/services/firestore_db_service.dart';

    enum AppMode {DEBUG, RELEASE}

    class UserRepository implements AuthBase{

    FirebaseAuthService _firebaseAuthService = locator<FirebaseAuthService>();
    FakeAuthenticationService _fakeAuthenticationService = locator<FakeAuthenticationService>();
    FirestoreDbService _firestoreDbService = locator<FirestoreDbService>();

    AppMode appMode = AppMode.RELEASE;
 
              @override
      Future<User> currentUser() async{
        if (appMode == AppMode.DEBUG) {
          return await _fakeAuthenticationService.currentUser();
        } else {
          return await _firebaseAuthService.currentUser();
        }
      }

      @override
      Future<User> signInAnonymously()  async{
        if (appMode == AppMode.DEBUG) {
          return await _fakeAuthenticationService.signInAnonymously();
        } else {
          return await _firebaseAuthService.signInAnonymously();
        }
      }

      @override
      Future<bool> signOut() async{
        if (appMode == AppMode.DEBUG){
          return await _firebaseAuthService.signOut();
        } else {
          return await _firebaseAuthService.signOut();
        }
      }

      @override
      Future<User> signInWithGoogle() async{
        if (appMode == AppMode.DEBUG) {
          return await _fakeAuthenticationService.signInWithGoogle();
        } else {
          User _user = await _firebaseAuthService.signInWithGoogle();
          bool _sonuc = await _firestoreDbService.saveUser(_user);
          if (_sonuc) {
            return _user; 
          }else return null;
          }
      }

      @override
      Future<User> signInWithFacebook() async{
        if (appMode == AppMode.DEBUG) {
          return await _fakeAuthenticationService.signInWithFacebook();
        } else {
          User _user = await _firebaseAuthService.signInWithFacebook();
          bool _sonuc = await _firestoreDbService.saveUser(_user);
          if (_sonuc) {
            return _user; 
          }else return null;
          }
      }

      @override
      Future<User> createUserWithEmailandPassword(String email, String sifre) async{
          if (appMode == AppMode.DEBUG) {
          return await _fakeAuthenticationService.createUserWithEmailandPassword(email, sifre);
        } else {
          User _user = await _firebaseAuthService.createUserWithEmailandPassword(email, sifre);
          bool _sonuc = await _firestoreDbService.saveUser(_user);
          if (_sonuc) {
            return _user; 
          }else return null;
          }
          
        }

      @override
      Future<User> signInWithEmailandPassword(String email, String sifre) async{
        if (appMode == AppMode.DEBUG) {
          return await _fakeAuthenticationService.signInWithEmailandPassword(email, sifre);
        } else {
          return await _firebaseAuthService.signInWithEmailandPassword(email, sifre);
        }
      }

    }

user_model.dart :

    import 'package:cloud_firestore/cloud_firestore.dart';
    import 'package:flutter/material.dart';
    import 'package:flutter/cupertino.dart';

    class User {
    final String userID;
    String email;
    String userName;
    String profilURL;
    DateTime createdAt;
    DateTime updatedAt;
    int seviye;

    User({@required this.userID, @required this.email});

    Map<String, dynamic> toMap(){
      return {
        "UserID" : userID,
        "email" : email,
        "userName" : userName ?? '',
        "profilURL" : profilURL ?? '',
        "createdAt" : createdAt ?? FieldValue.serverTimestamp(),
        "updatedAt" : updatedAt ?? FieldValue.serverTimestamp(),
        "seviye" : seviye ?? 1,
      };
    }

    User.fromMap(Map<String, dynamic> map):
      userID = map['userID'],
      email = map['email'],
      userName = map['userName'],
      profilURL = map['profilURL'],
      createdAt = (map['createdAt'] as Timestamp).toDate(),
      updatedAt = (map['updatedAt']as Timestamp).toDate(),
      seviye = map['seviye'];

    @override
    String toString() {
      return 'User{userID: $userID, email: $email, userName: $userName, profilURL: $profilURL, createdAt: $createdAt, updatedAt: $updatedAt, seviye: $seviye}';
    }


    }

Screenshot