Unable to start activity ComponentInfo Attempt to invoke virtual method on a null object reference

There are two activities in the app, in the second activity I have a textView and a button. Even though I have initialized the variables by findViewById but in both the cases it is showing the message attempt to invoke on a null pointer object. I have searched and read many answer which says that may be there is any other view with same id but in my case it is the only view with this id.

class SecondActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

//        val resultName = intent.getStringExtra("name")
        val result = findViewById<TextView>(R.id.textView3)
        result.text = getString(R.string.resDisplay)
        val replay = findViewById<Button>(R.id.button3)
        replay?.setOnClickListener {
            b1.text = ""
            b2.text = ""
            b3.text = ""
            b4.text = ""
            b5.text = ""
            b6.text = ""
            b7.text = ""
            b8.text = ""
            b9.text = ""
            b1.isEnabled = true
            b2.isEnabled = true
            b3.isEnabled = true
            b4.isEnabled = true
            b5.isEnabled = true
            b6.isEnabled = true
            b7.isEnabled = true
            b8.isEnabled = true
            b9.isEnabled = true
            val intent = Intent(this, MainActivity::class.java)
            startActivity(intent)
        }
    }

and this is my xml file of second layout

<TextView
        android:id="@+id/textView3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:hint="@string/player_2_x"
        android:layout_marginTop="200dp"
        android:textSize="24sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/play_again"
        android:layout_marginTop="16dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView3" />