Попытка вызвать виртуальный метод по нулевой ссылке на объект (метод String equals) Kotlin Version

Question

Я прошел через некоторые ответы, относящиеся к теме, но в приведенном ниже коде я явно использую любой метод String, и, следовательно, я не могу выяснить фактическую причину ошибки. Код для файла MainScreenAdapter.kt:

    package adapters

import android.content.Context
import android.os.Bundle
import android.support.v4.app.FragmentActivity
import android.support.v7.widget.RecyclerView
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.RelativeLayout
import android.widget.TextView
import com.example.champion.echo_12.R
import fragments.SongPlayingFragment
import fragments.Songs

**class MainScreenAdapter(_songDetails: ArrayList<Songs>, _context: Context) :RecyclerView.Adapter<MainScreenAdapter.MyViewHolder>()** {


    var songDetails: ArrayList<Songs>? = null
    var mContext: Context? = null


    init {
        this.songDetails = _songDetails
        this.mContext = _context
    }
    override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
        val songObject = songDetails?.get(position)

        holder.trackTitle?.text = songObject?.songTitle
        holder.trackArtist?.text = songObject?.artist
        holder.contentHolder?.setOnClickListener {
            //Toast.makeText(mContext,songObject?.songTitle+" is Playing",Toast.LENGTH_SHORT).show()
            val songPlayingFragment = SongPlayingFragment()
            val args = Bundle()
            args.putString("songArtist", songObject?.artist)
            args.putString("songTitle", songObject?.songTitle)
            args.putString("path", songObject?.songData)
            //to int required here
            args.putInt("songID",songObject?.songID?.toInt() as Int)
            args.putInt("songPosition", position)
            args.putParcelableArrayList("songData", songDetails)
            songPlayingFragment.arguments = args

            (mContext as FragmentActivity).supportFragmentManager
                    .beginTransaction()
                    .replace(R.id.details_fragment, songPlayingFragment)
                    .addToBackStack("SongPlayingFragment")
                    .commit()
        }
    }


    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
        **val itemView = LayoutInflater.from(parent.context)
                .inflate(R.layout.row_custom_mainscreen_adapter, parent, false)**

        return MyViewHolder(itemView)

    }
    override fun getItemCount(): Int {

        if (songDetails == null) {
            return 0
        }

        else {
            return (songDetails as ArrayList<Songs>).size
        }
    }

    class MyViewHolder(view: View) : RecyclerView.ViewHolder(view) {
        /*Declaring the widgets and the layout used*/
        var trackTitle: TextView? = null
        var trackArtist: TextView? = null
        var contentHolder: RelativeLayout? = null
        /*Constructor initialisation for the variables*/
        init {
            trackTitle = view.findViewById(R.id.trackTitle) as TextView
            trackArtist = view.findViewById(R.id.trackArtist) as TextView
            contentHolder = view.findViewById(R.id.contentRow) as RelativeLayout
        }
    }
}


Line 56 and Line 16(Bold marked **) are subjected to the error condition.

Вызов класса MainScreenAdapter ().

package fragments
import adapters.MainScreenAdapter
import android.app.Activity
import android.content.Context
import android.os.Bundle
import android.provider.MediaStore
import android.support.v4.app.Fragment
import android.support.v7.widget.DefaultItemAnimator
import android.support.v7.widget.LinearLayoutManager
import android.support.v7.widget.RecyclerView
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageButton
import android.widget.RelativeLayout
import android.widget.TextView
import com.example.champion.echo_12.R




private const val ARG_PARAM1 = "param1"
private const val ARG_PARAM2 = "param2"

/**
 * A simple [Fragment] subclass.
 *
 */
class MainScreenFragment : Fragment() {

    var getSongsList: ArrayList<Songs>? = null
    var nowPlayingBottomBar: RelativeLayout? = null
    var playPauseButton: ImageButton? = null
    var songTitle: TextView? = null
    var visibleLayout: RelativeLayout? = null
    var noSongs: RelativeLayout? = null
    var recyclerView: RecyclerView? = null
    var myActivity: Activity? = null
    var _mainScreenAdapter: MainScreenAdapter? = null

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        // Inflate the layout for this fragment
        val view = inflater!!.inflate(R.layout.fragment_main_screen, container, false)

        visibleLayout = view?.findViewById(R.id.visibleLayout)
        noSongs = view?.findViewById(R.id.noSongs)
        nowPlayingBottomBar = view?.findViewById(R.id.hiddenBarMainScreen)
        songTitle = view?.findViewById(R.id.songTitleMainScreen)
        playPauseButton = view?.findViewById(R.id.playPauseButton)
        recyclerView = view?.findViewById(R.id.contentMain)

        return view
        //return inflater.inflate(R.layout.fragment_main_screen, container, false)
    }

    override fun onAttach(context: Context?) {
        super.onAttach(context)
        myActivity=context as Activity
    }

    override fun onAttach(activity: Activity?) {
        super.onAttach(activity)
        myActivity=activity
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)

        getSongsList=getSongsFromPhone()
        _mainScreenAdapter= MainScreenAdapter(getSongsList as ArrayList<Songs>,myActivity as Context)

        val _mLayoutManager=LinearLayoutManager(myActivity)
        recyclerView?.layoutManager=_mLayoutManager
        recyclerView?.itemAnimator=DefaultItemAnimator()
        recyclerView?.adapter=_mainScreenAdapter

    }



    fun getSongsFromPhone(): ArrayList<Songs>{

        var arrayList = ArrayList<Songs>()
        var contentResolver = myActivity?.contentResolver
        var songUri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI
        var songCursor = contentResolver?.query(songUri, null, null, null, null)

        if (songCursor != null && songCursor.moveToFirst()) {
            val songId = songCursor.getColumnIndex(MediaStore.Audio.Media._ID)
            val songTitle = songCursor.getColumnIndex(MediaStore.Audio.Media.TITLE)
            val songArtist = songCursor.getColumnIndex(MediaStore.Audio.Media.ARTIST)
            val songData = songCursor.getColumnIndex(MediaStore.Audio.Media.DATA)
            val dateIndex = songCursor.getColumnIndex(MediaStore.Audio.Media.DATE_ADDED)

            while (songCursor.moveToNext()) {
                var currentId = songCursor.getLong(songId)
                var currentTitle = songCursor.getString(songTitle)
                var currentArtist = songCursor.getString(songArtist)
                var currentData = songCursor.getString(songData)
                var currentDate = songCursor.getLong(dateIndex)

                arrayList.add(Songs(currentId, currentTitle, currentArtist, currentData, currentDate))
            }
        }
        return arrayList


    }
}

Если бы кто-нибудь мог помочь мне указать причину для нулевой ссылки, я был бы очень благодарен.