Execute (Call) function if value is not empty in ASP.Net MVC

Hi,

I am trying to implement remote validations

Everything is working fine

But the major issue is that if designation value is empty then IsAlreadySigned method is not calling

As per as my need i need to call that when Designation value is not empty

[Remote("IsAlreadySigned", "Register", HttpMethod = "POST", ErrorMessage = "Already exists.")]
public string Designation { get; set; }

[HttpPost]
public JsonResult IsAlreadySigned(string Designation)
{
    return null;
    // return Json(IsUserAvailable(UserEmailId));
}