Flutter Firestore "_CastError (Null check operator used on a null value)" Error

I am getting an error like this:

Why could this be? How can I solve it?

Codes:

FirebaseAuth _auth = FirebaseAuth.instance;
FirebaseFirestore _firestore = FirebaseFirestore.instance;

// ...

_auth.createUserWithEmailAndPassword(
  email: _emailController.text,
  password: _passwordController.text,
);
_firestore.collection("Users").doc(_auth.currentUser!.uid).set({
  "ID": _auth.currentUser?.uid,
  "Email": _emailController.text,
  "Phone": _phoneController.text,
  "Name": _nameController.text,
  "Surname": _surnameController.text,
  "Photo": "https://firebasestorage.googleapis.com/v0/b/teen-software-stock-tracking.appspot.com/o/default.jpg?alt=media&token=0eec2e1f-2ccf-4bda-8664-3d3f018621b3",
  "Level": 0,
  "ProductRight": 10,
  "AddedProduct": 0,
});

User is created in Firebase Auth but I can't write data to Firestore.