public async Task <Domain.Models.Referral> GetReferralByReferralCodeAsync(string referralCode)
{
if (string.IsNullOrEmpty(referralCode))
{
var exception = new ArgumentNullException(nameof(referralCode));
_log.Error("Input parameter is null.", exception);
throw exception;
}
return(await _referralRepository.GetByReferralCodeAsync(referralCode) ??
throw new CustomerNotFoundException($"Referral code for Customer with id '{referralCode}' not found."));
}