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());