What is the reason for this NullReferenceException?

None of my other Objects seem to be able to reference the script ItemManager, every time I call for a static variable from it, it returns null.

World -

Player -

Here is the first (of many) places I get the error:

     NullReferenceException: Object reference not set to an instance of an object
     Inventory.Start () (at Assets/Scripts/Player/Inventory.cs:58

     Line58: ItemSlot temp = new ItemSlot(ItemManager.EMPTY.ShallowCopy());

I think it has to do with the static variable EMPTY, however I believe I have it setup correctly:

 public static Item EMPTY;
     public static Item STONE;
     public static Item GRASS;
     public static Item BRICK;
     
     //************************************
 
     // Use this for initialization
 
     void Start () {
         Debug.Log ("Initalized");
         guiCon = gameObject.GetComponent ("GUIController") as GUIController;
         soundMan = gameObject.GetComponent ("SoundManager") as SoundManager;
         
         // *** Set new ***
         
         // *** Initialize Item *** 
         EMPTY = new Item("", 0 , 64, new Rect(0.25f,0.75f, 0.25f,0.25f), itemIcons, Item.ItemType.Empty,"DefaultItem");
             // MORE CODE AFTER...