public IActionResult CreateGroup([FromBody] GroupForCreationDto groupDto)
        {
            if (groupDto == null)
            {
                return(BadRequest());
            }

            if (!ModelState.IsValid)
            {
                return(BadRequest(ModelState));
            }

            var groupEntity = Mapper.Map <Entities.Group>(groupDto);

            _registrationRepository.AddGroup(groupEntity);

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

            var createdGroupToReturn = Mapper.Map <GroupDto>(groupEntity);

            return(CreatedAtRoute("GetGroup", new
                                  { id = createdGroupToReturn.Id }, createdGroupToReturn));
        }