Firebase Firestore .set is updating instead of cre

Question

I am using Android client to create new document.

Map<String, Object> city = new HashMap<>();
city.put("name", "Los Angeles");
city.put("state", "CA");
city.put("country", "USA");

db.collection("cities").document("LA")
        .set(city)
        .addOnSuccessListener(new OnSuccessListener<Void>() {
            @Override
            public void onSuccess(Void aVoid) {
                Log.d(TAG, "DocumentSnapshot successfully written!");
            }
        })
        .addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                Log.w(TAG, "Error writing document", e);
            }
        });

This is my security rule

service cloud.firestore {
  match /databases/{database}/documents {
    match /cities/{city} {
      allow create: if (request.auth.uid != null);
      allow update: if (request.auth.uid != null) && !("country" in request.writeFields) );
    }
  }
}

As you see from security rules, update can happen only when the document does not contain "country" field. Create rule is straightforward.

In this example, I do not have the document "LA" in the collection and when I test it, I get PERMISSION DENIED error. Tweaking the update rule confirms, .set() is calling update rule.

How do I make .set call "create" rule exclusively?