Particle system MinMaxCurve problem

I have a specifc problem with particle system , I'm controlling the particle system via script , the problem comes up when I try to edit any MinMaxCurve in any module as shown below :

 using System.Collections;
 using UnityEngine;
 
 [RequireComponent(typeof(ParticleSystem))]
 public class PSTest : MonoBehaviour {
 
     ParticleSystem MyPS ;
 
     void Start () {
         
         MyPS = gameObject.GetComponent<ParticleSystem>();
 
         ParticleSystem.MainModule MyPSMain = MyPS.main;
 
         AnimationCurve ACTemp = new AnimationCurve (new Keyframe[] {
             new Keyframe (0, 1) , new Keyframe (1, 0) });
 
         MyPSMain.startSize = new ParticleSystem.MinMaxCurve ( 1 , ACTemp ); 
 
     }
 
 }

when I try script in the editor it works fine and no exception is thrown but when I run the project on android device the application exit and stop working after some tests I found that this line is making the issue :

 MyPSMain.startSize = new ParticleSystem.MinMaxCurve ( 1 , ACTemp ); 

So I try something else :

 using System.Collections;
 using UnityEngine;
 
 [RequireComponent(typeof(ParticleSystem))]
 public class PSTest : MonoBehaviour {
 
     ParticleSystem MyPS ;
 
     void Start () {
         
         MyPS = gameObject.GetComponent<ParticleSystem>();
 
         ParticleSystem.MainModule MyPSMain = MyPS.main;
 
         AnimationCurve ACTemp = new AnimationCurve (new Keyframe[] {
             new Keyframe (0, 1) , new Keyframe (1, 0) });
 
         ParticleSystem.MinMaxCurve SizeCurve = MyPSMain.startSize;
         SizeCurve.curveMultiplier = 1;
         SizeCurve.curve = ACTemp;
 
     }
 
 }

but what happens is the value of curve constant is working but the curve itself isnt assign to the start size , I though that I was taking value by reference when doing that , but when I debug I noticed that the start size have a value of null for both Min and Max Curve