public IActionResult Insert([FromBody] User value)
        {
            if (value is null)
            {
                return(BadRequest("value is null."));
            }

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

            UserContract.Add(value);
            return(CreatedAtRoute("GetUser", new { controller = "User", id = value.Id }, value));
        }