public IHttpActionResult Post(GroupModel newGroup)
        {
            if (newGroup == null)
            {
                throw new ArgumentNullException("Parameter could not be null", "newGroup");
            }

            if (!_groupService.ContainsGroupName(newGroup))
            {
                var groupToAdd = _groupMapper.Map(newGroup);
                _groupService.Add(groupToAdd);
                return(Ok());
            }
            return(BadRequest(string.Format("Group {0} already exist!", newGroup.Name)));
        }