java.lang.IllegalStateException at android.media.MediaPlayer : Android MediaPlayer Error

     --------- beginning of crash

2021-06-29 12:40:18.925 2968-2968/com.example.myapplication2 E/AndroidRuntime: FATAL EXCEPTION: main

    Process: com.example.myapplication2, PID: 2968

    java.lang.RuntimeException: Unable to stop service com.example.myapplication2.Util.AffirmationRingtoneService@4ce3875: java.lang.IllegalStateException

        at android.app.ActivityThread.handleStopService(ActivityThread.java:4201)

        at android.app.ActivityThread.access$2000(ActivityThread.java:224)

        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1924)

        at android.os.Handler.dispatchMessage(Handler.java:107)

        at android.os.Looper.loop(Looper.java:224)

        at android.app.ActivityThread.main(ActivityThread.java:7562)

        at java.lang.reflect.Method.invoke(Native Method)

        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)

        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)

     Caused by: java.lang.IllegalStateException

        at android.media.MediaPlayer._stop(Native Method)

        at android.media.MediaPlayer.stop(MediaPlayer.java:1418)

        at com.example.myapplication2.Util.AffirmationRingtoneService.stopMediaPlayerAfterAlarmFire(AffirmationRingtoneService.kt:72)

        at com.example.myapplication2.Util.AffirmationRingtoneService.onDestroy(AffirmationRingtoneService.kt:81)

        at android.app.ActivityThread.handleStopService(ActivityThread.java:4177)

        at android.app.ActivityThread.access$2000(ActivityThread.java:224) 

        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1924) 

        at android.os.Handler.dispatchMessage(Handler.java:107) 

        at android.os.Looper.loop(Looper.java:224) 

        at android.app.ActivityThread.main(ActivityThread.java:7562) 

        at java.lang.reflect.Method.invoke(Native Method) 

        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539) 

        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950) 

2021-06-29 12:40:18.931 2968-2968/com.example.myapplication2 E/MQSEventManagerDelegate: failed to get MQSService.

2021-06-29 12:40:18.932 2968-2968/com.example.myapplication2 E/CustomActivityOnCrash: App has crashed, executing CustomActivityOnCrash's UncaughtExceptionHandler

    java.lang.RuntimeException: Unable to stop service com.example.myapplication2.Util.AffirmationRingtoneService@4ce3875: java.lang.IllegalStateException

        at android.app.ActivityThread.handleStopService(ActivityThread.java:4201)

        at android.app.ActivityThread.access$2000(ActivityThread.java:224)

        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1924)

        at android.os.Handler.dispatchMessage(Handler.java:107)

        at android.os.Looper.loop(Looper.java:224)

        at android.app.ActivityThread.main(ActivityThread.java:7562)

        at java.lang.reflect.Method.invoke(Native Method)

        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)

        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)

     Caused by: java.lang.IllegalStateException

        at android.media.MediaPlayer._stop(Native Method)

        at android.media.MediaPlayer.stop(MediaPlayer.java:1418)

        at com.example.myapplication2.Util.AffirmationRingtoneService.stopMediaPlayerAfterAlarmFire(AffirmationRingtoneService.kt:72)

        at com.example.myapplication2.Util.AffirmationRingtoneService.onDestroy(AffirmationRingtoneService.kt:81)

        at android.app.ActivityThread.handleStopService(ActivityThread.java:4177)

        at android.app.ActivityThread.access$2000(ActivityThread.java:224) 

        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1924) 

        at android.os.Handler.dispatchMessage(Handler.java:107) 

        at android.os.Looper.loop(Looper.java:224) 

        at android.app.ActivityThread.main(ActivityThread.java:7562) 

        at java.lang.reflect.Method.invoke(Native Method) 

        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539) 

        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950) 

java.lang.RuntimeException: Unable to instantiate activity ComponentInfo Kotlin Android

I found these in Warning in Manifest.xml::

".MainActivity" in <activity android:name=".MainActivity"> is not a concrete class.

In android Studio error log is as below:

java.lang.RuntimeException: Unable to instantiate activity ComponentInfo Kotlin Android
   Process: com.example.espl.myapplication22, PID: 9829
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.espl.myapplication22/com.example.espl.myapplication22.MainActivity}: java.lang.InstantiationException: java.lang.Class<com.example.espl.myapplication22.MainActivity> cannot be instantiated
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2398)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2547)
        at android.app.ActivityThread.access$1100(ActivityThread.java:151)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1398)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:157)
        at android.app.ActivityThread.main(ActivityThread.java:5603)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:774)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:652)
     Caused by: java.lang.InstantiationException: java.lang.Class<com.example.espl.myapplication22.MainActivity> cannot be instantiated
        at java.lang.Class.newInstance(Native Method)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1068)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2388)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2547)
        at android.app.ActivityThread.access$1100(ActivityThread.java:151)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1398)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:157)
        at android.app.ActivityThread.main(ActivityThread.java:5603)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:774)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:652)

SOLUTION:
Remove the abstract before the class decleration of MainActivity