Instantiating a prefabs from an array of prefabs gives a NullReferenceException error

I'm trying to create an array of prefabs from my prefabs folder so that whenever a new enemy is added (and there will be a lot, so I don't want to have to add each one in the inspector manually), I can instantiate it from the array. In my script, I'm attempting to instantiate random enemies from the array, but instead, it gives me a NullReferenceException error, telling me that the object reference is not set to an instance of an object. How do I get it to use to random prefabs selected in the array for the object reference ? Here's the code :

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class EnemySpawner : MonoBehaviour
 {
     public GameObject ActiveEnemy, LeftSupportEnemy, RightSupportEnemy, InactiveEnemy; //the four positions of the enemies I'm trying to spawn
     public GameObject[] allLeps; //the gameobject array
     public int totalLeps = 0; //an int to keep track of the array size
     public GameObject EAttackPos, ELeftSupPos, ERightSupPos, EInactivePos; //use for their transform.positions later, these are set in the inspector
 
     private void Start()
     {
         allLeps = Resources.LoadAll<GameObject>("Prefabs") as GameObject[]; //this seems to be working properly since I can see the array getting populated by prefabs in the inspector
         foreach (GameObject leps in allLeps)
         {
             totalLeps++; //this number goes up to the expected amount
         }
     }
 
     public void SetRandomOpponents() //this gets called in a seperate BattleManager script
     {
         Debug.Log("Starting to set opponents"); //for testing purposes. It doesn't even show up, the nullreferenceexception happens first.
         int E1 = Random.Range(0, totalLeps);
         int E2 = Random.Range(0, totalLeps);
         int E3 = Random.Range(0, totalLeps);
         int E4 = Random.Range(0, totalLeps); //getting a random position in the array
 
         GameObject ActiveEnemy = Instantiate(allLeps[E1]) as GameObject;
         GameObject LeftSupportEnemy = Instantiate(allLeps[E2]) as GameObject;
         GameObject RightSupportEnemy = Instantiate(allLeps[E3]) as GameObject;
         GameObject InactiveEnemy = Instantiate(allLeps[E4]) as GameObject; //trying to make it so that it instantiates a random gameobject from the array, but they aren't being set
 
 
         
         ActiveEnemy.transform.position = new Vector2(EAttackPos.transform.position.x, EAttackPos.transform.position.y);
         LeftSupportEnemy.transform.position = new Vector2(ELeftSupPos.transform.position.x, ELeftSupPos.transform.position.y);
         RightSupportEnemy.transform.position = new Vector2(ERightSupPos.transform.position.x, ERightSupPos.transform.position.y);
         InactiveEnemy.transform.position = new Vector2(EInactivePos.transform.position.x, EInactivePos.transform.position.y); //this is just to give their their proper positions
 
     }
 
 
 }