public IActionResult DeleteGroup(int id)
        {
            var groupEntity = _registrationRepository.GetGroup(id, includeSubgroups: false);

            if (groupEntity == null)
            {
                return(NotFound());
            }

            _registrationRepository.DeleteGroup(groupEntity);

            if (!_registrationRepository.Save())
            {
                return(StatusCode(500, "A problem happened while handling your request."));
            }

            return(NoContent());
        }