firebase not creating data when user signs for first time - flutter

Question

when new user signIn, In firebase Authentication tab it is showing users details.
but not adding the function to firestore.
google signIn code:
Future<UserCredential> signInWithGoogle() async {
showDialog(
context: context,
builder: (context) {
return const Center(child: CircularProgressIndicator());
});
final _auth = FirebaseAuth.instance;
// Trigger the authentication flow
final GoogleSignInAccount? googleUser = await GoogleSignIn().signIn();
// Obtain the auth details from the request
final GoogleSignInAuthentication? googleAuth =
await googleUser?.authentication;
// Create a new credential
final credential = GoogleAuthProvider.credential(
accessToken: googleAuth?.accessToken,
idToken: googleAuth?.idToken,
);
final UserCredential authResult =
await _auth.signInWithCredential(credential);
final user = authResult.user;
if (authResult.additionalUserInfo!.isNewUser) {
if (user != null) {
await DbServices().addNewUser(FirebaseAuth.instance.currentUser!.uid);
}
}
removeLoading();
// Once signed in, return the UserCredential
return await FirebaseAuth.instance.signInWithCredential(credential);
}
removeLoading() {
return Navigator.of(context).pop();
}
}
**this is addNewUser function:**
Future addNewUser(useruid) async {
int heartid = await updateHeartId();
print('updated Heart Id $heartid....................');
await usersCollection.doc(useruid).set({
'user name': FirebaseAuth.instance.currentUser!.displayName,
'uid': useruid,
'heartId': heartid,
'total hearts': 0,
'ringed': false,
'Timestamp': FieldValue.serverTimestamp(),
'profile pic': '',
'todayRinged': false,
'ringedDay': DateTime.now().day,
});
}
when I looked into it, firebase isn't adding the function addNewUser in firestore.
I don't understand what's happening here.
when I signIn for first time the app crashes saying :
> StateError(Bad state: cannot get a field on a DocumentSnapshotPlatform
> which does not exist)
why is the addNewUser function not adding to firestore?