What does the !! (double-bang) operator do in Kotlin and why is it needed?

Hi everyone! I just started learning Kotlin after Java and came across a strange `!!` operator. For example, I saw this code:\n\n```kotlin\nval name: String? = getUserName()\nval length = name!!.length\n```\n\nI understand that `?` means the variable can be null. But why is `!!` needed? It seems like if I'm sure the value is not null, I can just use `?.` or write `if (name != null)`. And if I'm wrong, I'll get a NullPointerException — that's bad!\n\nIn Java, I'm used to checking for null with `if`, but here there's some aggressive operator. Maybe it's a crutch for those too lazy to write checks? Or are there situations where `!!` is actually justified? Please explain what it does, how it works, and whether it should be used at all in real projects. Code examples are welcome.