[android] problem z onActivityResult()

Witam. Mam problem z przechwyceniem zrobionego zdjęcia i nie mam pojęcia czym jest on spowodowany. Może ktoś pomóc w naprawie tego? Stawiam pierwsze kroki w androidzie.
content_main.xml

<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/cont"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.example.pp.lab3.MainActivity"
    tools:showIn="@layout/activity_main">
<Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="300dp"
        android:layout_marginEnd="216dp"
        android:onClick="kliknij2"
        android:text="baton 2"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent" />
```
main_acitvity.java
```java
public void kliknij2(View view)
    {
        Intent intencja2=new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        startActivityForResult(intencja2,REQUEST_IMAGE_CAPTURE);

    }
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data)
    {
        Bundle extras=data.getExtras();
        Bitmap imageBitmap=(Bitmap) extras.get("data");
        RelativeLayout lay= (RelativeLayout) findViewById(R.id.cont);
        lay.setBackground(new BitmapDrawable(getResources(),imageBitmap));

    }
```
android studio w debugu pokazuje problem z tą linijką, ale nie mam pojęcia dlaczego:

```java
lay.setBackground(new BitmapDrawable(getResources(),imageBitmap));
```
logi:
```java
FATAL EXCEPTION: main
                  Process: com.example.pp.lab3, PID: 3577
                  java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1, result=-1, data=Intent { act=inline-data (has extras) }} to activity {com.example.pp.lab3/com.example.pp.lab3.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.RelativeLayout.setBackground(android.graphics.drawable.Drawable)' on a null object reference
                      at android.app.ActivityThread.deliverResults(ActivityThread.java:3574)
                      at android.app.ActivityThread.handleSendResult(ActivityThread.java:3617)
                      at android.app.ActivityThread.access$1300(ActivityThread.java:151)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1352)
                      at android.os.Handler.dispatchMessage(Handler.java:102)
                      at android.os.Looper.loop(Looper.java:135)
                      at android.app.ActivityThread.main(ActivityThread.java:5254)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at java.lang.reflect.Method.invoke(Method.java:372)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.RelativeLayout.setBackground(android.graphics.drawable.Drawable)' on a null object reference
                      at com.example.pp.lab3.MainActivity.onActivityResult(MainActivity.java:56)
                      at android.app.Activity.dispatchActivityResult(Activity.java:6192)
                      at android.app.ActivityThread.deliverResults(ActivityThread.java:3570)
                      at android.app.ActivityThread.handleSendResult(ActivityThread.java:3617) 
                      at android.app.ActivityThread.access$1300(ActivityThread.java:151) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1352) 
                      at android.os.Handler.dispatchMessage(Handler.java:102) 
                      at android.os.Looper.loop(Looper.java:135) 
                      at android.app.ActivityThread.main(ActivityThread.java:5254) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at java.lang.reflect.Method.invoke(Method.java:372) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
```

Musisz zawołać wcześniej setContentView.