In C# MVC why is throwing an exception when Razor model from ViewModel

Question

I am using MVC with C#,

Here is my ViewModel class:

public class MyViewModel
{        
    public MySqlConnectionStringBuilder Con { get; set; }// Without this property everything is working fine.
    public string PrName { get; set; }
    public string Aky { get; set; }
    public string Sky { get; set; }
}

My Razor View:

@model MySQLDB
<form class="form-horizontal myform" action="/MyAction">
@Html.TextBoxFor(mode => Model.PrName, new { @class = "form-control", @required = "required", @placeholder = "Name your backup" })
@Html.TextBoxFor(model => model.Con.Server, new { @class = "form-control", @required = "required", @placeholder = "Enter host address" })
@Html.TextBoxFor(model => model.Aky, new { @Value = "ALOJUS", @class = "form-control", @required = "required" })
@Html.TextBoxFor(model => model.Sky, new { @Value = "IJSHS9KSDFES", @class = "form-control", @required = "required" })
<button type="submit" name="ActionName" value="Connect" class="btn btn-default btn-connect">Connect &raquo;</button>
</form>

My Ajax Post:

$('.myform').on("submit", function (e) {
        e.preventDefault();            
        $.post('/MyAction', $(this).serializeArray(), function (resp) {
            alert(resp);
        });
    });

My Controller:

[HttpGet]
    public ActionResult MyAction()
    {
        return View(new MyViewModel())
    }
    [HttpPost]
    public async Task<JsonResult> MyAction(MyViewModel model)
    {
        var taskResult = await Task.Run(() => {
            //do something
            return Json(new {message="success" }, JsonRequestBehavior.AllowGet);
        });
        return taskResult;
    }

But, getting error like Object reference not set to instance of an object. Even it doesn't go into my Controller breakpoint.

Answers at What is a NullReferenceException, and how do I fix it? are not fully address my question, because in my scenario there are no empty or null values from the posted form, if i remove the MySqlConnectionStringBuilder property then everything is working fine. object deserialization is not working when i use MySqlConnectionStringBuilder property in my viewmodel class. Here MySqlConnectionStringBuilder is class defined in the meta DLL MySql.Data.MySqlClient