How to implement Banner Ad in Android Studio Kotlin? I followed the instructions in the google documentation but it doesn't work, the app closes when trying to open the activity where the ad would be, the whole app is made with recyclerview, the error is: java.lang.NullPointerException: findViewById(R.id.adViewComoSeJuega) must not be null This is my Activity: class ComoSeJuegaActivity : AppCompatActivity() { lateinit var mAdView : AdView override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState)...