Script Throws Errors Unless GameObject is Selected

I get a NullReferenceException when trying to view the count of a list after it has been modified via script.

You can recreate this issue by attaching the following script to any object, using the 'A' and 'D' keys to modify the list, and the 'E' key which is supposed to print the count.

You will find that if you select the GameObject to which the script is attached in the hierarchy, there will be no errors. Once the object is deselected, errors occur.

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3. using System.Collections.Generic;
4.  
5. [System.Serializable]
6. public class Slot
7. {
8.     public List<GameObject> layers = new List<GameObject>();
9. }
10.  
11. public class Test : MonoBehaviour
12. {
13.     public Slot[] slots;
14.  
15.     private IEnumerator Start() // A coroutine is used because it otherwise gives an error
16.     {
17.         slots = new Slot[7];
18.         yield return new WaitForSeconds(0.1f);
19.         slots[3].layers.Add(null);
20.     }
21.  
22.     private void Update()
23.     {
24.         if (Input.GetKeyDown(KeyCode.A)) Rotate(false);
25.         if (Input.GetKeyDown(KeyCode.D)) Rotate(true);
26.         if (Input.GetKeyDown(KeyCode.E)) Debug.Log(slots[0].layers.Count);
27.     }
28.  
29.     private void Rotate(bool forward)
30.     {
31.         for (int i = 0; i < slots.Length; i++)
32.         {
33.             try
34.             {
35.                 if (forward) slots[6 - i] = slots[6 - i - 1];
36.                 else slots[i] = slots[i + 1];
37.             }
38.             catch
39.             {
40.                 if (forward) slots[6 - i] = null;
41.                 else slots[i] = null;
42.             }
43.         }
44.     }
45. }

 

Code (csharp):

1.  
2. void OnEnable() {
3.  if(slots == null) {
4.   slots = new Slot[7];
5.   for(var i = 0; i < slots.Length; i++){
6.     slots[i] = new Slot();
7.   }
8.  }
9. }
10.