public async Task <NewslettersFilteredCollectionViewModel> GetNewslletersFilteredCollection(int?newsletterId, string newsletterEmail, int pageNumber, int pageSize)
        {
            var newsletters = await newsletterService.GetNewslettersCollection(newsletterId, newsletterEmail, pageNumber, pageSize);

            var result = mapper.Map <IEnumerable <NewsletterViewModel> >(newsletters);

            return(new NewslettersFilteredCollectionViewModel
            {
                Newsletters = result,
                PaginationViewModel = new PaginationViewModel
                {
                    CurrentPage = pageNumber,
                    ItemsPerPage = pageSize,
                    TotalItems = await newsletterService.GetNewslettersCollectionCount(newsletterId, newsletterEmail)
                },
                NewsletterId = newsletterId,
                NewsletterEmail = newsletterEmail
            });
        }