로그인 기능이 제대로 작동하지않습니다.

현재 주어진대로 코드를 짜넣어 진행하였으나 구글계정으로 로그인까지만 되며 그이후 탭페이지로 넘어가지않고 그대로 로그인페이지에 머물러있습니다 에디터에서 따로 오류문구는 떠오르지 않고있습니다ㅠㅠ

import 'package:flutter/material.dart';
import 'package:flutter_signin_button/flutter_signin_button.dart';
import 'package:google_sign_in/google_sign_in.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:instagramclon/tab_page.dart';

class LoginPage extends StatelessWidget {
  final GoogleSignIn _googleSignIn = GoogleSignIn();
  final FirebaseAuth _auth = FirebaseAuth.instance;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text('Instagram Clon',
                style: TextStyle(fontSize: 40.0, fontWeight: FontWeight.bold)),
            Padding(
              padding: EdgeInsets.all(50.0),
            ),
            SignInButton(
              Buttons.Google,
              onPressed: () {
                _handleSingIn().then((user) {
                 Navigator.pushReplacement(context,
                 MaterialPageRoute(builder: (context) => TabPage(user)));
                });
              },
            ),
          ],
        ),
      ),
    );
  }

  Future<FirebaseUser> _handleSingIn() async {
    GoogleSignInAccount googleUser = await _googleSignIn.signIn();
    GoogleSignInAuthentication googleAuth = await googleUser.authentication;
    FirebaseUser user = await _auth.signInWithCredential(
        GoogleAuthProvider.getCredential(
            idToken: googleAuth.idToken, accessToken: googleAuth.accessToken));
    print("signed in " + user.displayName);
    return user;
  }
}