code: @Nullable
      public List<String> getAllStoreSkus(@NotNull final String appstoreName) {
          if (TextUtils.isEmpty(appstoreName)) {
              throw SkuMappingException.newInstance(SkuMappingException.REASON_STORE_NAME);
          }
  
          Map<String, String> skuMap = sku2storeSkuMappings.get(appstoreName);
          return skuMap == null ? null :
                  Collections.unmodifiableList(new ArrayList<String>(skuMap.values()));
      }
docs: Returns a list of SKU for a store.
  
  @param appstoreName The app store name.
  @return list of SKU that mapped to the store. Null if the store has no mapped SKUs.
  @throws java.lang.IllegalArgumentException If the store name is null or empty.
  @see #mapSku(String, String, String)