Kotlinを使ってAndroidでSMS送信時に、getSystemServiceがNULLになります

//@Composable
fun onClickMailButton(view:View) {
    val number = "080????????"  // 送信先電話番号

    try {
        val smsManager:SmsManager
        if (Build.VERSION.SDK_INT>=23) {
            //if SDK is greater that or equal to 23 then
            //this is how we will initialize the SmsManager
            smsManager = this.getSystemService(SmsManager::class.java)
        }
        else{
            //if user's SDK is less than 23 then
            //SmsManager will be initialized like this
            smsManager = SmsManager.getDefault()
        }
        smsManager.sendTextMessage(number, null, "メッセージ", null, null)
        // on below line we are displaying a toast message for message send,
        Toast.makeText(applicationContext, "Message Sent", Toast.LENGTH_LONG).show()

    } catch (e: Exception) {
        // on catch block we are displaying toast message for error.
        Toast.makeText(applicationContext, "Please enter all the 　data.."+e.message.toString(), Toast.LENGTH_LONG)
            .show()
    }
}