在服务中使用MainActivity函数会产生错误，为什么？

问：

我是android的新手。我需要在服务中使用MainActivity函数才能再次访问服务的onstart命令

我期望的是第一个服务会因为 on create 方法而运行，但由于操作不是“ACTION_PLAY”服务将运行 MainActivity.start（） 函数，然后服务再次启动，我得到 println（“action play working”）

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

    val intent = Intent(this,myService::class.java)
    intent.putExtra("action","ACTION_STOP")
    startService(intent)

}

fun start(){
    val intent = Intent(this,myService::class.java)
    intent.putExtra("action","ACTION_PLAY")
    startService(intent)
}

}

class myService: Service() {
override fun onBind(intent: Intent?): IBinder? {
    return null
}

override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {

    val action = intent?.getStringExtra("action")
    if (action == "ACTION_PLAY"){
        println("action play working")
    }
    else{
        MainActivity().start()
    }



    return super.onStartCommand(intent, flags, startId)
}

}

但它给了我这个错误

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.isililkproje, PID: 9526
java.lang.RuntimeException: Unable to start service com.example.isililkproje.myService@95959e6 with Intent { cmp=com.example.isililkproje/.myService (has extras) }: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
    at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:3314)
    at android.app.ActivityThread.-wrap21(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1565)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6077)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
    at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:106)
    at com.example.isililkproje.MainActivity.start(MainActivity.kt:28)
    at com.example.isililkproje.myService.onStartCommand(myService.kt:19)
    at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:3297)
    at android.app.ActivityThread.-wrap21(ActivityThread.java) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1565) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:154) 
    at android.app.ActivityThread.main(ActivityThread.java:6077) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756) 

请给我解释一下为什么它会出错以及我该如何解决这个问题，谢谢