The function can't be unconditionally invoked because it can be 'null' in flutter

The function can’t be unconditionally invoked because it can be ‘null’. getting an error in this part auth.currentUser

 FirebaseAuth auth = FirebaseAuth.instance;
    final User user = await auth.currentUser();
    String uid = user.uid;
    await FirebaseFirestore.instance.collection('data').doc(uid).collection('data').doc();

>Solution :

try;

 FirebaseAuth auth = FirebaseAuth.instance;
final User user = await auth.currentUser;
String uid = user!.uid;
await FirebaseFirestore.instance.collection('data').doc(uid).collection('data').doc();