What type error is it?

Scripting C# & .NET
1

The error shows up after running the game 2 min.

ArgumentOutOfRangeException: Argument is out of range.
Parameter name: index
System.Collections.Generic.List`1[UnityEngine.Animator].get_Item (Int32 index) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Collections.Generic/List.cs:633)
RobotAI.RobotBodyPartAnimationTurnOn () (at Assets/BattleMap/RobotAI.cs:727)
CAT001EnterIdle.OnStateEnter (UnityEngine.Animator animator, AnimatorStateInfo stateInfo, Int32 layerIndex) (at Assets/Behaviour/CAT001EnterIdle.cs:16)

public class CAT001EnterIdle: StateMachineBehaviour {
   

     // OnStateEnter is called when a transition starts and the state machine starts to evaluate this state
    override public void OnStateEnter(Animator animator, AnimatorStateInfo stateInfo, int layerIndex) {
       
        // CAT enter idle mode
      
        // trigger robotbody part animation
        animator.GetComponent<RobotAI>().RobotBodyPartAnimationTurnOn();

    }


}

    public void RobotBodyPartAnimationTurnOn()
    {
   
        if (weaponAnimator[weaponSelected] != null)
            weaponAnimator[weaponSelected].SetTrigger(weapon[weaponSelected].RBPAnimeTrigger);                    

    }
2

Arguement out of range means you’re trying to access an index that doesn’t exist. So whatever weaponAnimator[weaponSelected] is trying to get doesn’t exist. A null check doesn’t work because it doesn’t even exist.