Is it possible to get the transform for Gizmos from the start method to keep the Gizmo's transform constant during runtime?

I created an enemy who can only move wit$$anonymous$$n a certain distance of their start location. I want to show that distance using OnDrawGizmos with the below code. But when I use the below, I get "NullReferenceException: Object reference not set to an instance of an object". It looks like it happens because the start method is not called before running the game. When I run the game, the cube follows the enemy around instead of staying in the initial enemy position. Is there a way to get the cube to stay at the initial enemy position instead of following the enemy?

 private Transform initialPosition;
 public float walkPointRange;
     
 void Start()
     {
         agent = GetComponent<NavMeshAgent>();
         initialPosition = transform;
     }
 
 void OnDrawGizmos()
     {
         Color colliderColor = Color.green;
         colliderColor.a = 0.2f;
         Gizmos.color = colliderColor;
         Gizmos.DrawCube(initialPosition.position, new Vector3(walkPointRange, 1, walkPointRange));
     }