ModelState.IsValid is true if password is empty string - asp.net-mvc

Question

I am passing login model to mvc4 default login method
[HttpPost]
[AllowAnonymous]
[ValidateAntiForgeryToken]
public ActionResult Login(LoginModel model, string returnUrl)
{
if (ModelState.IsValid && _webSecurity.login(model))
{
return RedirectToLocal(returnUrl);
}
// If we got this far, something failed, redisplay form
ModelState.AddModelError("", "The user name or password provided is incorrect.");
return View(model);
}
My Model looks like following
var _loginModel = new LoginModel
{
UserName = abc#gmail.com,
Password = ""
};
but ModelState.IsValid is returning true . I don't know why . Help me
Thanks in advance .
Edit
Here is my LoginModel
public class LoginModel
{
[Required]
[Display(Name = "User name")]
public string UserName { get; set; }
[Required]
[DataType(DataType.Password)]
[Display(Name = "Password")]
public string Password { get; set; }
[Display(Name = "Remember me?")]
public bool RememberMe { get; set; }
}

Answer 1

The validation Attribute defined in the model will be apllied while Model Binding, u don't have to do this manualy.
[Required]
[StringLength(100, ErrorMessage = "The {0} must be at least {2} characters long.",MinimumLength = 6)]
[DataType(DataType.Password)]
[Display(Name = "Password")]
public string Password { get; set; }
For more complex validation you also could add a regex filter like this:
[RegularExpression(#"^[^\<\>]*$", ErrorMessage = "May not contain <,>")]
This would match windows group policy password filter for example:
(?=^.{6,255}$)((?=.*\d)(?=.*[A-Z])(?=.*[a-z])|(?=.*\d)(?=.*[^A-Za-z0-9])(?=.*[a-z])|(?=.*[^A-Za-z0-9])(?=.*[A-Z])(?=.*[a-z])|(?=.*\d)(?=.*[A-Z])(?=.*[^A-Za-z0-9]))^.*