public Task <string> Add(FilterAggregate filter)
        {
            if (filter == null)
            {
                throw new ArgumentNullException(nameof(filter));
            }

            filter.Id             = Guid.NewGuid().ToString();
            filter.CreateDateTime = filter.CreateDateTime;
            _filters.Add(filter.Copy());
            return(Task.FromResult(filter.Id));
        }