public async Task HandleAsync(CreatePhoneBookCommand command)
        {
            var phoneBook = await _phoneBookRepository.GetPhoneBookByNameAsync(command.Name);

            if (phoneBook != null)
            {
                throw new ValidateException("Phone book already exists");
            }
            await _phoneBookRepository.AddAsync(new Entities.PhoneBookAggregateRoot(command.Name));

            await _phoneBookRepository.SaveAsync();
        }