dialogTemplate validationRules for dropdownList

                @Html.EJ().DropDownListFor(o => o.EmployeeID, (Syncfusion.JavaScript.Models.DropDownListProperties)ViewBag.ddl).DropDownListFields(o=>o.Text("id").Value("id")).ValidationRules(v=>v.AddRule("required", true)) 

I have:

<ejs-dropdownlist width="200" id="EmployeeID" dataSource="@ViewBag.Employees" filtering="onfiltering" placeholder="Wybierz Pracownika" allowFiltering="true" filterBarPlaceholder="Wyszukaj"
                                      headerTemplate="@Html.Raw("<div class=\"header\"> Imię i Nazwisko</span></div>)")"
                                      itemTemplate="@Html.Raw("<div class=\"name\"> ${Name} ${Surname} </div>")"
                                      valueTemplate="@Html.Raw("<div class=\"name\"> ${Name} ${Surname} </div>")"
                                      value="@ViewBag.selectedEmployees">
                        <e-dropdownlist-fields validationRules="@(new { required=true})" text="EmployeeID" value="EmployeeID"></e-dropdownlist-fields>
                    </ejs-dropdownlist>

I need to validate if dropdownlist is selected from list. Default is null. I want to prevent close dialog if dropdownlist is not selected.

Flag validationRules don't work here.

In Grid when i add:

<e-grid-column validationRules="@(new { required=true})" allowEditing="false" field="EmployeeID" width="80" headerText="EmployeeID" visible="false"></e-grid-column>

don't work too. Works only for input text.