public async Task <IEnumerable <ItemDto> > GetExchangeRatesAsync(string date)
        {
            if (!_dateValidationService.IsValid(date))
            {
                return(null);
            }

            var exchangeRatesRequested = await _exchangeRatesRepository.GetExchangeRatesAsync(date);

            var exchangeRatesComparative =
                await _exchangeRatesRepository.GetExchangeRatesAsync(_exchangeRateService.GetComparativeDate(date));

            return(_exchangeRateService.GetExchangeRateChanges(exchangeRatesRequested, exchangeRatesComparative));
        }