What does the !! (double exclamation mark) operator do in Kotlin and when should it be used?

Hello everyone! I just started learning Kotlin after Java and can't figure out the `!!` operator. Kotlin is praised for null safety, but here's some double exclamation mark that, as I understand, on the contrary, can cause a NullPointerException. I'm writing a small notes application. I have a function that searches for a user by ID in the database and returns their name. If the user is not found, it returns null. Here's an example code: ```kotlin fun getUserName(userId: Int): String? { // returns null if user not found return database.findUser(userId)?.name } ``` Then I call this function and want to display the name in a TextView: ```kotlin val name = getUserName(123) textView.text = name // Error: Type mismatch. Required: String, Found: String? ```