Question Creating enemies from spawn points in a JSON list

I'm new to C# and programming in general so bear with me. I'm trying to spawn enemies at coordinates based on a json list. I've made it work with one enemy but I want more enemies to be created based on the number of positions in the json file.

When I run this in Unity I get this error:
NullReferenceException: Object reference not set to an instance of an object
JsonUtils.Start () (at Assets/Scripts/JsonUtils.cs:38)

I've ran some debug lines before that line but I'm not quite sure what I'm looking at or how to fix it. I don't think it's parsing the json file correctly is my best guess.

Here's the JSON list:

Code (csharp):

1. {
2.   "positions":
3.   [
4.   [-151, 0.95, 133],
5.   [4, 5, 6]
6.   ]
7. }

I have a JsonUtils.cs script attached to an empty 'adversaryManager' object in Unity:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class Vector3Serialization
6. {
7.     public float x;
8.     public float y;
9.     public float z;
10. }
11.  
12. public class Vector3Positions
13. {
14.     public float[][] positions;
15. }
16.  
17.  
18. public class JsonUtils : MonoBehaviour
19. {
20.     public static TextAsset jsonAsset;
21.     public static string json;
22.  
23.     public static Vector3Positions vector3Positions;
24.     public static List<Vector3> positions = new List<Vector3>();
25.  
26.     private void Start()
27.     {
28.         jsonAsset = Resources.Load("adversaryPOS") as TextAsset;
29.         json = jsonAsset.text;
30.         vector3Positions = JsonUtility.FromJson<Vector3Positions>(json);
31.  
32.         Debug.Log("JSON contents: " + json);
33.         Debug.Log("vector3Positions: " + vector3Positions);
34.         Debug.Log("vector3Positions.positions: " + vector3Positions.positions);
35.  
36.         if (vector3Positions != null)
37.         {
38.             foreach (float[] position in vector3Positions.positions)
39.             {
40.                 positions.Add(new Vector3(position[0], position[1], position[2]));
41.             }
42.         }
43.         else
44.         {
45.             Debug.LogError("vector3Positions is null");
46.         }
47.     }
48. }

I also have an AdversaryManager.cs script attached to that same gameobject. In that script I have a prefab attached to the GameObject 'adversaryPrefab'.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class AdversaryManager : MonoBehaviour
6. {
7.     public GameObject adversaryPrefab;
8.  
9.  
10.     private List<Vector3> positions;
11.  
12.     void Start()
13.     {
14.         positions = JsonUtils.positions;
15.         SpawnAdversaries1(positions);
16.     }
17.  
18.     private void SpawnAdversaries1(List<Vector3> positions)
19.     {
20.         Debug.Log("Positions count: " + positions.Count);
21.         foreach (Vector3 position in positions)
22.         {
23.             if (position != null)
24.             {
25.                 GameObject go = Instantiate(adversaryPrefab, position, Quaternion.identity);
26.                 go.transform.parent = transform;
27.             }
28.             else
29.             {
30.                 Debug.LogError("Position is null");
31.             }
32.         }
33.     }
34. }

Here's what my debug log says:
JSON contents: {
"positions":
[
[-151, 0.95, 133],
[4, 5, 6]
]
}
UnityEngine.Debug:Log (object)
JsonUtils:Start () (at Assets/Scripts/JsonUtils.cs:32)

vector3Positions: Vector3Positions
UnityEngine.Debug:Log (object)
JsonUtils:Start () (at Assets/Scripts/JsonUtils.cs:33)

vector3Positions.positions:
UnityEngine.Debug:Log (object)
JsonUtils:Start () (at Assets/Scripts/JsonUtils.cs:34)

Any help is greatly appreciated, I'm going crazy trying to get it to work.