오류가 나서 문의 드립니다.

Future<FirebaseUser> _handleSignIn()  async{
  GoogleSignInAccount googleUser;
  googleUser = await _googleSignIn.signIn();
  GoogleSignInAuthentication googleAuth = await googleUser.authentication;
  FirebaseUser user = await _auth.signInWithCredential(GoogleAuthProvider.getCredential(idToken: googleAuth.idToken, accessToken: googleAuth.accessToken));
  return user;

ompiler message:
lib/login_page.dart:40:25: Error: A value of type 'AuthResult' can't be assigned to a variable of type 'FirebaseUser'.
 - 'AuthResult' is from 'package:firebase_auth/firebase_auth.dart' ('/C:/src/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-0.15.4/lib/firebase_auth.dart').
 - 'FirebaseUser' is from 'package:firebase_auth/firebase_auth.dart' ('/C:/src/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-0.15.4/lib/firebase_auth.dart').
    FirebaseUser user = await _auth.signInWithCredential(