Soomla Error for android

I have created my own store front with the soomla tutorials. I’m getting an error when I start my game. The script with my store stuff is:

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
namespace Soomla.Store.Example {
	/// <summary>
	/// This class defines our game's economy, which includes virtual goods, virtual currencies
	/// and currency packs, virtual categories
	/// </summary>
	public class IAPitems : IStoreAssets{
		/// <summary>
		/// see parent.
		/// </summary>
		public int GetVersion() {
			return 0;
		}
		/// <summary>
		/// see parent.
		/// </summary>
		public VirtualCurrency[] GetCurrencies() {
			return new VirtualCurrency[]{CREDITS_CURRENCY};
		}
		/// <summary>
		/// see parent.
		/// </summary>
		public VirtualGood[] GetGoods() {
			return new VirtualGood[] {RAINBOW_CHICKEN, HALLOWEEN_CHICKEN, SANTA_CHICKEN, NO_ADS_LTVG};
		}
		/// <summary>
		/// see parent.
		/// </summary>
		public VirtualCurrencyPack[] GetCurrencyPacks() {
			return new VirtualCurrencyPack[] {SMALL_CREDITS_PACK, MEDIUM_CREDITS_PACK, BIG_CREDITS_PACK, MEGA_CREDITS_PACK};
		}
		/// <summary>
		/// see parent.
		/// </summary>
		public VirtualCategory[] GetCategories() {
			return new VirtualCategory[]{GENERAL_CATEGORY};
		}
		/** Static Final Members **/
		public const string CREDITS_CURRENCY_ITEM_ID = "currency_credits";
		public const string SMALL_CREDITS_PACK_PRODUCT_ID = "android.test.refunded";
		public const string MEDIUM_CREDITS_PACK_PRODUCT_ID = "android.test.canceled";
		public const string BIG_CREDITS_PACK_PRODUCT_ID = "android.test.purchased";
		public const string MEGA_CREDITS_PACK_PRODUCT_ID = "2500_pack";
		public const string RAINBOW_CHICKEN_ITEM_ID = "rainbow_chicken";
		public const string HALLOWEEN_CHICKEN_ITEM_ID = "halloween_chicken";
		public const string SANTA_CHICKEN_ITEM_ID = "santa_chicken";
		public const string NO_ADS_LIFETIME_PRODUCT_ID = "no_ads";
		/** Virtual Currencies **/
		public static VirtualCurrency CREDITS_CURRENCY = new VirtualCurrency(
			"Credits", // name
			"", // description
			CREDITS_CURRENCY_ITEM_ID // item id
			);

		/** Virtual Currency Packs **/
		public static VirtualCurrencyPack SMALL_CREDITS_PACK = new VirtualCurrencyPack(
			"5000 Credits", // name
			"Test refund of an item", // description
			"5kCredits", // item id
			5000, // number of currencies in the pack
			CREDITS_CURRENCY_ITEM_ID, // the currency associated with this pack
			new PurchaseWithMarket(SMALL_CREDITS_PACK_PRODUCT_ID, 0.99)
			);
		public static VirtualCurrencyPack MEDIUM_CREDITS_PACK = new VirtualCurrencyPack(
			"27500 Credits", // name
			"Test cancellation of an item", // description
			"27kCredits", // item id
			27500, // number of currencies in the pack
			CREDITS_CURRENCY_ITEM_ID, // the currency associated with this pack
			new PurchaseWithMarket(MEDIUM_CREDITS_PACK_PRODUCT_ID, 4.99)
			);
		public static VirtualCurrencyPack BIG_CREDITS_PACK = new VirtualCurrencyPack(
			"55000 Credits", // name
			"Test purchase of an item", // description
			"55kCredits", // item id
			55000, // number of currencies in the pack
			CREDITS_CURRENCY_ITEM_ID, // the currency associated with this pack
			new PurchaseWithMarket(BIG_CREDITS_PACK_PRODUCT_ID, 9.99)
			);
		public static VirtualCurrencyPack MEGA_CREDITS_PACK = new VirtualCurrencyPack(
			"120000 Credits", // name
			"Test item unavailable", // description
			"120kCredits", // item id
			120000, // number of currencies in the pack
			CREDITS_CURRENCY_ITEM_ID, // the currency associated with this pack
			new PurchaseWithMarket(MEGA_CREDITS_PACK_PRODUCT_ID, 19.99)
			);

		/** LifeTimeVGs **/
		// Note: create non-consumable items using LifeTimeVG with PuchaseType of PurchaseWithMarket
		public static VirtualGood RAINBOW_CHICKEN = new LifetimeVG(
			"Rainbow Chicken", // name
			"Unlock the Rainbow Chicken", // description
			"rainbow_chick", // item id
			new PurchaseWithVirtualItem(CREDITS_CURRENCY_ITEM_ID, 15000)); // the way this virtual good is purchased
		public static VirtualGood HALLOWEEN_CHICKEN = new LifetimeVG(
			"Halloween Chicken", // name
			"Unlock the Halloween Chicken", // description
			"halloween_chick", // item id
			new PurchaseWithVirtualItem(CREDITS_CURRENCY_ITEM_ID, 30000)); // the way this virtual good is purchased
		public static VirtualGood SANTA_CHICKEN = new LifetimeVG(
			"Santa Chicken", // name
			"Unlock the Santa Chicken", // description
			"santa_chicken", // item id
			new PurchaseWithVirtualItem(CREDITS_CURRENCY_ITEM_ID, 50000)); // the way this virtual good is purchased
		public static VirtualGood NO_ADS_LTVG = new LifetimeVG(
			"No Ads", // name
			"No More Ads!", // description
			"no_ads", // item id
			new PurchaseWithMarket(NO_ADS_LIFETIME_PRODUCT_ID, 0.99)); // the way this virtual good is purchased

		/** Virtual Categories **/
		// The muffin rush theme doesn't support categories, so we just put everything under a general category.
		public static VirtualCategory GENERAL_CATEGORY = new VirtualCategory(
			"General", new List<string>(new string[] { RAINBOW_CHICKEN_ITEM_ID, HALLOWEEN_CHICKEN_ITEM_ID, SANTA_CHICKEN_ITEM_ID })
			);
	}
}

The error im getting is:
NullReferenceException: Object reference not set to an instance of an object
Soomla.Store.SoomlaStore.Initialize (IStoreAssets storeAssets) (at Assets/Plugins/Soomla/Store/SoomlaStore.cs:88)
HomeScreen.Start () (at Assets/Scripts/HomeScreen.cs:12)

The line on the HomeScreen script for the error is:

SoomlaStore.Initialize(new Soomla.Store.Example.IAPitems());

I do not know the Soomla framework or plugin, but by looking at their code, it looks like the reference comes from this code inside the Initialize method (SoomlaStore.cs:88):

StoreEvents.Instance.onSoomlaStoreInitialized("", true);

The StoreEvents component is probably added to some game object or prefab that should have been created before accessing it.

Make sure you have this object in your scene.