Problema con Script2

Hola de nuevo
Tengo hecho este cogido :

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class GameDB : MonoBehaviour {

public Sprite[] sprites;
public static List<Item> itemList = new List<Item>();
// Use this for initialization
void Start () {

    //ITEM CREATION
    Item i0 = new Item();
    i0.name = "Apple";
    i0.type = Item.Type.consumable;
    i0.sprite = sprites[0];
    itemList.Add(i0);

    //ITEM CREATION
    Item i1 = new Item();
    i1.name = "Water";
    i1.type = Item.Type.consumable;
    i1.sprite = sprites[1];
    itemList.Add(i1);

    //ITEM CREATION
    Item i2 = new Item();
    i2.name = "Bread";
    i2.type = Item.Type.consumable;
    i2.sprite = sprites[2];
    itemList.Add(i2);

    //ITEM CREATION
    Item i3 = new Item();
    i3.name = "Bandages";
    i3.type = Item.Type.consumable;
    i3.sprite = sprites[3];
    itemList.Add(i3);

    //ITEM CREATION
    Item i4 = new Item();
    i4.name = "Medkit";
    i4.type = Item.Type.consumable;
    i4.sprite = sprites[4];
    itemList.Add(i4);
}

// Update is called once per frame
void Update () {
	
}
}

pero al darle al play en unity me pone este error:
NullReferenceException
GameDB.Start () (at Assets/Scripts/GameDB.cs:14)
A que se debe?