This AsyncTask class should be static or leaks might occur

MainActivity.kt

import android.os.AsyncTask
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import com.burhan.studentattendance.R
import java.lang.ref.WeakReference


class MainActivity : AppCompatActivity() {

    private var mJustAVariable = 0
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        MyAsyncTask(this).execute()
    }

    private class MyAsyncTask internal constructor(context: MainActivity) : AsyncTask<Void, Void, String>() {

        private val activityReference: WeakReference<MainActivity> = WeakReference(context)

        override fun doInBackground(vararg params: Void): String {
            // do some long running task...
            return "task finished"
        }

        override fun onPostExecute(result: String) {
            // get a reference to the activity if it is still there
            val activity = activityReference.get()
            if (activity == null || activity.isFinishing) return
            // access Activity member variables or modify the activity's UI
            activity.mJustAVariable = 123
        }
    }

}