i can't change the intensity of chromatic aberration

I am trying to change the intensity of chromatic aberration. I've looked at a ton of guides and can't seem to figure out what I'm doing wrong.

fixing the error is not so important for me as understanding how to change the intensity using a script.

here is my script

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.Rendering.PostProcessing;
5.  
6. public class postprocessing : MonoBehaviour
7. {
8.     private PostProcessVolume pv;
9.     private ChromaticAberration ca;
10.  
11.  
12.     void Start()
13.     {
14.         pv = GetComponent<PostProcessVolume>();
15.         pv.profile.TryGetSettings(out ca);
16.     }
17.  
18.  
19.     public void ChromaticAberrationOnOff(bool on)
20.     {
21.         if (on)
22.         {
23.             ca.active = true;
24.         }
25.         else
26.         {
27.             ca.active = false;
28.         }
29.     }
30. }
31.  

here is the error -
NullReferenceException: Object reference not set to an instance of an object
postprocessing.Start ()

 

Sorry for creating a useless thread. It was necessary to delete everything and write again exactly the same script. And everything worked.