asyncLoad method Null safety

Implementation

@override
Future<String?> asyncLoad() async {
  try {
    final SearchResult searchResult = await productQuery.getSearchResult();
    final ProductList productList = productQuery.getProductList();
    partialProductList.clear();
    if (searchResult.products != null) {
      productList.setAll(searchResult.products!);
      productList.totalSize = searchResult.count!;
      partialProductList.add(productList);
      await DaoProduct(localDatabase).putAll(searchResult.products!);
    }
    DaoProductList(localDatabase).put(productList);
    return null;
  } catch (e) {
    return e.toString();
  }
}