transform.position assign attempt for 'Cubie' is not valid. Input position is { NaN, NaN, NaN }.

So here's some background information, I am trying to create this explosion effect of "cubie's". I have one object called enemy that when he collides with a bullet it destroys itself and instantiates another object called EnemyDeathAnimation which is not really an animation but a gameObject that replicates an explosion effect based on this tutorial: http://gamedevelopment.tutsplus.com/tutorials/how-to-make-an-object-shatter-into-smaller-fragments-in-unity--gamedev-11795

when I play the game and shoot the enemies occasionally I get the NaN error. I think it may be caused by the sphere used in the explosion effect instantiating and interfering with other objects. If anyone could shed some light on how to avoid/fix the error that would be great. If there is any better way of creating the explosion effect I would be more than happy to scratch this method and do it that way.

Enemy Script: using UnityEngine; using System.Collections;

 public class EnemyCubeScript : MonoBehaviour 
 {
     public GameObject deathAnimation;
 
     private float fadeTimer = 1.9f;
     private Transform player;
     private NavMeshAgent nav;
 
     void OnTriggerEnter (Collider col)
     {
         if(col.tag == "Bullet")
         {
             GameObject deathAnimationClone = Instantiate(deathAnimation, transform.position, transform.rotation) as GameObject; //instantiates deathAnimation gameObject
             Destroy (gameObject); //destroy self
             Destroy (deathAnimationClone, fadeTimer); 
             Destroy (col.gameObject); //destroy bullet
         }
     }
     void Awake () {
         player = GameObject.FindGameObjectWithTag ("Player").transform;
         nav = GetComponent <NavMeshAgent> ();
     }
     
     void Update () {
         nav.SetDestination (player.position);
     }
 }