Android TextToSpeech in Kotlin

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/edittext_input"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="8"
        android:gravity="center_horizontal"
        android:hint="Enter a message" />

    <Button
        android:id="@+id/button_speak"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Speak" />

</LinearLayout>

MainActivity.kt

package com.example.android.texttospeech

import android.os.Build
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.speech.tts.TextToSpeech
import android.util.Log
import kotlinx.android.synthetic.main.activity_main.*
import java.util.*

class MainActivity : AppCompatActivity(), TextToSpeech.OnInitListener {

    private var tts: TextToSpeech? = null

    override fun onInit(status: Int) {
        if (status == TextToSpeech.SUCCESS) {
            // set UK English as language for tts
            val result = tts!!.setLanguage(Locale.UK)

            if (result == TextToSpeech.LANG_MISSING_DATA || result == TextToSpeech.LANG_NOT_SUPPORTED) {
                Log.e("TTS", "The Language specified is not supported!")
            } else {
                button_speak.isEnabled = true
            }
        } else {
            Log.e("TTS", "Initialization Failed!")
        }
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        button_speak.isEnabled = false
        tts = TextToSpeech(this, this)

        button_speak.setOnClickListener { speakOut() }
    }

    private fun speakOut() {
        var message = edittext_input.text.toString()
        if (message.isNullOrBlank()) message = "Please enter a message"

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            tts!!.speak(message, TextToSpeech.QUEUE_FLUSH, null, "")
        } else {
            @Suppress("DEPRECATION")
            tts!!.speak(message, TextToSpeech.QUEUE_FLUSH, null)
        }
    }

    override fun onDestroy() {
        // Shut down TTS
        if (tts != null) {
            tts!!.stop()
            tts!!.shutdown()
        }

        super.onDestroy()
    }
}

Thanks