Save call Null and Elvis Operator 

fun main(args : Array<String>){
    val text : String? = null
    //akses cek null
    if(text != null){
        val textLength = text.length
    }
    //safe call
    text?.length
    
    //elvis Operator ?:
    val textLength = text?.length :? 7
    //val textLength = if(text != null) text.length else 7
    
    //non-null assertion (!!) tidak disarankan karena dapat mengakses null
    val textLength = text!!.length
    
}