AndroidでAdMobの初期化時にクラッシュする ref: https://qiita.com/masaibar/items/848362349442026063e2

AndroidManifest.xml

<manifest>
    <application>
           :
          (中略)
           :
           <meta-data
            android:name="com.google.android.gms.ads.APPLICATION_ID"
            android:value="ADMOB_APP_ID"/>

    </application>
</manifest>

Application.kt

MobileAds.initialize(this, ADMOB_APP_ID)

file0.txt

// implementation 'com.google.firebase:firebase-ads:16.0.1' ←アップデート前

implementation 'com.google.firebase:firebase-ads:17.1.2'

file2.txt

2019-01-01 17:15:30.332 30306-30306/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.masaibar.sample, PID: 30306
    java.lang.RuntimeException: Unable to get provider com.google.android.gms.ads.MobileAdsInitProvider: java.lang.IllegalStateException: 

    ******************************************************************************
    * The Google Mobile Ads SDK was initialized incorrectly. AdMob publishers    *
    * should follow the instructions here: https://goo.gl/fQ2neu to add a valid  *
    * App ID inside the AndroidManifest. Google Ad Manager publishers should     *
    * follow instructions here: https://goo.gl/h17b6x.                           *
    ******************************************************************************


        at android.app.ActivityThread.installProvider(ActivityThread.java:6445)
        at android.app.ActivityThread.installContentProviders(ActivityThread.java:5987)
        at android.app.ActivityThread.handleBindApplication(ActivityThread.java:5902)
        at android.app.ActivityThread.access$1100(ActivityThread.java:200)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1656)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6718)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: java.lang.IllegalStateException: