How to handle Firebase Database error in iOS? #AskFirebase

I need to handle "Permission Denied" error differently from all other errors.

In Android I've done it: (Kotlin)

override fun onCancelled(error: DatabaseError) {
    if (error.code == DatabaseError.PERMISSION_DENIED) {
        // Warn user
    }
}

In iOS I have only:

someDbReference.observe(.childAdded, with: { data in 
    // Do something
}, withCancel: { err in
    // err is Error
    print((err as NSError).code) // 1
    // Which error? O_o
})

How to determine error type? I've read whole documentation, and I think that err.localizedDescription == "Permission Denied" is a really bad way.