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))); }