尝试在kotlin中使用.startsWith()和.contains()方法时出错

val str = "Hello World"
val startsWithHello = str.startsWith("Hello")
val containsWorld = str.contains("World")

val str: String? = null
val startsWithHello = str?.startsWith("Hello")
val containsWorld = str?.contains("World")

import kotlin.text.startsWith
import kotlin.text.contains

fun main() {
    val str = "Hello World"
    val startsWithHello = str.startsWith("Hello")
    val containsWorld = str.contains("World")
}