cheatButton not accepted

Android Programming (5th Edition) 7. Your Second Activity
1

I get the message “Only safe (?.) or non-null asserted (!!.) calls are allowed on a nullable receiver of type Button?” in this line:
“binding.cheatButton.setOnClickListener {”

When I try to run the application I get the message:
" * Unresolved reference: cheatButton"

I have no idea how to fix this problem. Anyone?

this is my xml file:


   <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:id="@+id/previous_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/previous_button"
            app:icon="@drawable/arrow_left"
            app:iconGravity="start"/>

        <Button
            android:id = "@+id/cheat_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/cheat_button"/>

        <Button
            android:id="@+id/next_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/next_button"
            app:icon="@drawable/arrow_right"
            app:iconGravity="end"/>

    </LinearLayout>

This is my MainActivity.kt file:

        binding.nextButton.setOnClickListener{
            quizViewModel.moveToNext()
            updateQuestion()
        }

        binding.previousButton.setOnClickListener{
            //currentIndex = (currentIndex - 1) % questionBank.size
            //val questionTextResId = questionBank[currentIndex].textResId
            //binding.questionTextView.setText(questionTextResId)
            quizViewModel.moveToPrevious()
            updateQuestion()
        }

        binding.cheatButton.setOnClickListener {
            val intent = Intent(this, CheatActivity::class.java)
            startActivity(intent)
        }