Make SKU mapping lazy.

you could modify the conditional such that you don't need this null check here to simplify the return cases (3 cases to 2):

    if (sku2storeSkuMappings == null || sku2StoreSkuMappings.get(appstoreName) == null) {
        return null; // or Collections.emptyList();
    }
    Map<String, String> skuMap = sku2storeSkuMappings.get(appstoreName);
    List skuMapAsList = new ArrayList<String>(skuMap.values());
    return Collections.unmodifiableList(skuMapAsList);