Back end returning Nullable object must have a value

I am really not sure where this error is coming, if it's from the database or the backend. I am not even sure where to start to look

{
    List<Data.Models.UserInfo> users = new List<Data.Models.UserInfo>();
    using (CEntities dbContext = new CEntities())
    {
        List<User> entities = new List<User>();

        entities = dbContext.User.Where(c => !string.IsNullOrEmpty(c.LastName)).ToList();
        foreach (var entity in entities)
        {
            users.Add(new Data.Models.UserInfo(entity));
        }
    }
    return Json(users);
}
catch (Exception e)
{
    logger.Error(e);
    return Content(HttpStatusCode.InternalServerError, new { Error = e.Message });
}