Delete default value from deopdownlist

[Mohammad]

Hello
when my data source fill from controller by default select one value fordeopdownlist and i set null for value of deopdownlist i dot want select any value.

$(document).ready(function () {

 

        var baseAddress = window.parent.document.location + "Home/";

        var viewModel = kendo.observable({

            userDataSource: new kendo.data.DataSource({

                transport: {

                    read: {

                        url: baseAddress + "GetUsers",

                        dataType: "json",

                    }

                }

            }),

            SelectedRole: null,

            SelectedUser: null,

            accessValue: null,

            Roles: [],

            Accesses: [],

 

        });