Recycler View не получает Отображение содержимого

У меня проблемы с реализацией Recyclerview. Вот моя деталь об ошибке

       E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.internshala.test1, PID: 5181
              java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView$LayoutManager.onMeasure(android.support.v7.widget.RecyclerView$Recycler, android.support.v7.widget.RecyclerView$State, int, int)' on a null object reference
                  at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:1694)
                  at android.view.View.measure(View.java:22097)
                  at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
                  at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
                  at android.view.View.measure(View.java:22097)
                  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6606)
                  at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1514)
                  at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1167)
                  at android.widget.LinearLayout.onMeasure(LinearLayout.java:687)
                  at android.view.View.measure(View.java:22097)
                  at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
                  at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
                  at android.view.View.measure(View.java:22097)
                  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6606)
                  at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
                  at android.view.View.measure(View.java:22097)
                  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6606)
                  at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1514)
                  at android.widget.LinearLayout.measureVertical(LinearLayout.java:806)
                  at android.widget.LinearLayout.onMeasure(LinearLayout.java:685)
                  at android.view.View.measure(View.java:22097)
                  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6606)
                  at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
                  at com.android.internal.policy.DecorView.onMeasure(DecorView.java:727)
                  at android.view.View.measure(View.java:22097)
                  at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2448)
                  at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1530)
                  at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1787)
                  at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1418)
                  at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6800)
                  at android.view.Choreographer$CallbackRecord.run(Choreographer.java:968)
                  at android.view.Choreographer.doCallbacks(Choreographer.java:780)
                  at android.view.Choreographer.doFrame(Choreographer.java:715)
                  at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:954)
                  at android.os.Handler.handleCallback(Handler.java:790)
                  at android.os.Handler.dispatchMessage(Handler.java:99)
                  at android.os.Looper.loop(Looper.java:164)
                  at android.app.ActivityThread.main(ActivityThread.java:6620)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:518)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:822)

I / Process: отправка сигнала. PID: 5181 SIG: 9 Приложение прекращено.

вот код, который используется для вызова класса адаптера

        if (araayList == null || (araayList.isEmpty() as Boolean)) {
        Toast.makeText(this, "its empty", Toast.LENGTH_SHORT).show()
    } else {
        this.displayingPostAdapters = DisplayingPostAdapters(araayList, this)



        recylerView = findViewById<RecyclerView>(R.id.recyclerView)
        mlayoutManager == LinearLayoutManager(this)
        (mlayoutManager as LinearLayoutManager).orientation = LinearLayoutManager.VERTICAL
        recylerView?.layoutManager = mlayoutManager
        recylerView?.itemAnimator = DefaultItemAnimator()
        recylerView?.adapter = displayingPostAdapters
        recylerView?.setHasFixedSize(true)
        this.displayingPostAdapters!!.notifyDataSetChanged()

    }

}

пожалуйста, попробуйте дать предложения по устранению этой ошибки, спасибо