public static IQueryable<Tracker.Core.Data.User> ByFirstName(this IQueryable<Tracker.Core.Data.User> queryable, string firstName, params string[] additionalValues)
        {
            var firstNameList = new List<string> { firstName };

            if (additionalValues != null)
                firstNameList.AddRange(additionalValues);
            else
                firstNameList.Add(null);

            if (firstNameList.Count == 1)
                return queryable.ByFirstName(firstNameList[0]);

            return queryable.ByFirstName(firstNameList);
        }
        public static IQueryable<PetShop.Core.Data.Account> ByFirstName(this IQueryable<PetShop.Core.Data.Account> queryable, string firstName, params string[] additionalValues)
        {
            var firstNameList = new List<string> { firstName };

            if (additionalValues != null)
                firstNameList.AddRange(additionalValues);

            if (firstNameList.Count == 1)
                return queryable.ByFirstName(firstNameList[0]);

            return queryable.ByFirstName(firstNameList);
        }