'NullReferenceException: Object reference not set of an object' When calling a method.

Whenever I call the coroutine spawnDelay found in this script:

     public string spawnPos;
     public GameObject DataKeeper;
     public SpawnHelperScript SHS;
     public bool canSpawn = false;
     public int spawnDelayTime = 2;
     public int testSpawn  = 5;
     GruntAI GAI;
 
     // Use this for initialization
     void Awake () {
         DataKeeper = GameObject.FindGameObjectWithTag("DataKeeper");
         SHS = DataKeeper.GetComponent<SpawnHelperScript>();
     }
     
     // Update is called once per frame
     void Update () {
 
     }
 
     public void spawnGrunt(int amount){
         Debug.Log ("spawnGrunt called!");
         GameObject newEnemy = (GameObject)Instantiate (grunt, transform.position, transform.rotation);
         GAI = newEnemy.GetComponent<GruntAI>();
         if (!SHS.midSpawned && SHS.enemyCount == 0) {
             SHS.enemyCount ++;
             SHS.midSpawned = true;
             GAI.Pos = "mid";
         } else if (SHS.midSpawned && (SHS.rightCount + SHS.leftCount) <= 0) {
             SHS.enemyCount ++;
             SHS.rightCount ++;
             GAI.Pos = "right";
         } else if (SHS.leftCount > SHS.rightCount) {
             SHS.enemyCount ++;
             SHS.rightCount ++;
             GAI.Pos = "right";
         } else if (SHS.leftCount < SHS.rightCount) {
             SHS.enemyCount ++;
             SHS.leftCount ++;
             GAI.Pos = "left";
         } else if (SHS.rightCount == SHS.leftCount) {
             int RandomNum = Mathf.RoundToInt(Random.value);
             if(RandomNum == 0){
                 SHS.enemyCount ++;
                 SHS.leftCount ++;
                 GAI.Pos = "left";
             }else if(RandomNum == 1){
                 SHS.enemyCount ++;
                 SHS.rightCount ++;
                 GAI.Pos = "right";
             }
         }
     }
 
     public IEnumerator spawnDelay(int D, int amount){
         for (int i = 0; i < amount; i++) {
             spawnGrunt(amount);
             yield return new WaitForSeconds (D);
         }
 
     }
 
 }

From this script:

 using UnityEngine;
 using System.Collections;
 
 public class SpawnHelperScript : MonoBehaviour {
     public int enemyCount;
     public int leftCount;
     public int rightCount;
     public bool midSpawned = false;
     public EnemySpawnScript ESC;
     public GameObject ES;
 
     void Awake () {
         ES = GameObject.FindGameObjectWithTag ("EnemySpawner");
         ESC = ES.GetComponent <EnemySpawnScript>();
         Debug.Log ("Awake called");
     }
 
     public void wave(int enemyNum, string type, int SpawnDelay){
         if (type == "grunt") {
             StartCoroutine (ESC.spawnDelay(SpawnDelay, enemyNum));
         } else {
             Debug.LogError ("Wave Enemy type non-existant!");
         }
     
     }
 
 }
 

Which is being called from this script:

 using UnityEngine;
 using System.Collections;
 
 public class waveScript : MonoBehaviour {
     public GameObject DataKeeper;
     public SpawnHelperScript SHS;
 
     // Use this for initialization
     void Awake () {
         DataKeeper = GameObject.FindGameObjectWithTag("DataKeeper");
         SHS = DataKeeper.GetComponent<SpawnHelperScript>();
         SHS.wave (5, "grunt");
     }
 
 }

It spits out this error:

 NullReferenceException: Object reference not set of an object SpawnHelperScript.wave (Int32 enemyNum, System.String type) (at Assets/Scripts/Game Scripts/SpawnHelperScript.cs:19)