Instantiated object gives NullReferenceException

Hi,

We have an event system that spawns Goblins via a GoblinManager like this:

 using UnityEngine;
 using System.Collections;
 
 public class EventGoblinWave : EventT {
     
     private GoblinManager mManager;
 
     public EventGoblinWave(GoblinManager aManager) : base("Goblin Wave")
     {        
         mManager = aManager;
         //spawn 3 goblins here
         for (int i = 0; i < 3; i++)
         {
             mManager.SpawnGoblin(new Vector3(5, 47, -7));
         }
     }
     
     public void Update()
     {
         base.Update();
     }
 }

now we want to spawn some from an object that is on the scene via the same GoblinManager and we do it like this:

 using UnityEngine;
 using System.Collections;
 public class GoblinHut : MonoBehaviour
 {
     public int HitPoints;
     
     private GoblinManager mManager;
     private MainGameLoop mMainGameLoop;
     private float mSpawnTimer;
     
     // Use this for initialization
     void Start () {
         HitPoints = 200;
         mSpawnTimer = -1;
         
         mMainGameLoop = GameObject.Find("MainGameLoop").GetComponent("MainGameLoop") as MainGameLoop;
         mManager = mMainGameLoop.GetGoblinManager();
     }
     
     // Update is called once per frame
     void Update ()
     {
         if (mManager == null)
         {
             mManager = mMainGameLoop.GetGoblinManager();
         }
         
         if (mSpawnTimer >= 2)
         {
             mManager.SpawnGoblin(transform.position);
             mSpawnTimer = 0;
         }
         else
         {
             mSpawnTimer += Time.deltaTime;
         }
     }
     
     public void GetHit(int aHitPointLoss)
     {
         if (HitPoints > 0)
         {
             HitPoints -= aHitPointLoss;
         }
     }
 }

when we spawn the object from the GoblinHut via the GoblinManager we get a NullReferenceException when the GoblinManager check if the goblin spawned is dead. It seems it's because the Start() has not been called when called from the GoblinHut. The thing I don't understand is that Start() is called when the event spawn them.

Here is the GoblinManager class:

 using UnityEngine;
 using System.Collections;
 
 public class GoblinManager : MonoBehaviour {
     
     private ArrayList mGoblins;
     public GameObject GoblinPrefab;
     private Object mMainLoop;
     
     public void SetMainLoop(Object aMainLoop)
     {
         mMainLoop = aMainLoop;
     }
     
     // Use this for initialization
     void Start () 
     {
         mGoblins = new ArrayList();
     }
     
     public void SpawnGoblin(Vector3 aPos)
     {
         GameObject newGoblin = Instantiate(GoblinPrefab, aPos, Quaternion.identity) as GameObject;
         newGoblin.active = true;
         if (newGoblin != null)
         {
             mGoblins.Add(newGoblin);
         }
     }
     
     // Update is called once per frame
     public void Update () 
     {
         for (int i = 0; i < mGoblins.Count; i++)
         {
             GameObject obj = (GameObject)mGoblins[i];
             if (obj.active)
             {
                 EnemyGoblin goblin = obj.GetComponent<EnemyGoblin>();
                 if (goblin != null)
                 {
                     if (goblin.IsDead())
                     {
                         Destroy((Object)mGoblins[i]);
                         mGoblins.RemoveAt(i);
                         break;
                     }
                 }
             }
         }
     }
 }

Thanks for you help