Can't set an int from seperate script

Hi I’m making a weapon grouping system for a mechwarrior style game.

I want the system to set the weapons group to an integer of 1,2,3 or 4 by getting the int “GroupNum” and weapon “Pwep” from a UI button’s “ButtonValue” script when clicked, then changing the weapon’s int “WeaponGroup” with the “SetForTYPE” function in weapon array.
.

The problem I am having is that when the “SetForTYPE” function is called the the “GroupNum” int (which is set to the correct int from the “ButtonValue” script) returns a NullExceptionError and does not set the weapon’s “GroupNum”.

Button Value script

public class ButtonValue : MonoBehaviour {

    ButtonValue thisButton;
    public bool projectile;
    UIPWeaponValue Pwep;

void Start () { 
        
        thisButton = this.GetComponent<ButtonValue>();
        //gets the weapon value of selected weapon if the bool is set to that type
        if (projectile == true) {
            Pwep = transform.GetComponentInParent<UIPWeaponValue>();            
        }
}
  public void SetGroup() {

        FindObjectOfType<WeaponArray>().button = thisButton;
        //sets the selected weapons and calls the relevent fuction in weaponArray
        if (Pwep !=null) {
            FindObjectOfType<WeaponArray>().weapon = Pwep.gameObject;
            FindObjectOfType<WeaponArray>().SetForProjectile();
        }
}

}
Weapon Array Script

public class WeaponArray : MonoBehaviour {

    List<int> WeaponGroup = new List<int>();
    
    public ButtonValue button;
    public GameObject weapon;

	void Start () {
        WeaponGroup.Add(1);
        WeaponGroup.Add(2);
        WeaponGroup.Add(3);
        WeaponGroup.Add(4);
    }
    public void SetForProjectile() {
        print(button.GroupNum);
        weapon.GetComponent<WeaponProjectileScript>().weaponGroup = button.GroupNum;
    }

It seems like the script cant find the weapons “weaponGroup” int but I dont know why, the “weapon” group int is a public int .

Have fixed the problem, I was getting the wrong object in the “SetGroup” function so it was getting the button value instead of the weapon value I changes that and now it works fine.