ModernUi graph is not showing in the application

Question

I am trying to display the stack column chart in my project. somehow i am not able to display. i am not able to figure out what is wrong with it.below is the picture what i wanted to do.

[Stacked column chart][1] [1]: https://i.stack.imgur.com/guOrY.png Here is my wpf code

<chart:StackedColumnChart
            ChartTitle="Stacked Column Chart with Dynamic Series"
            ChartSubTitle="Which types of errors and warnings appears most">
        <chart:StackedColumnChart.SeriesTemplate>
            <DataTemplate>
                <chart:ChartSeries
                        SeriesTitle="ok"
                        DisplayMember="dataName"
                        ValueMember="dataValue"
                        ItemsSource="{Binding Path=Bars}" />
            </DataTemplate>
        </chart:StackedColumnChart.SeriesTemplate>
    </chart:StackedColumnChart>

and this my class

public class MainViewModel
{

    public ObservableCollection<ChartSeries> Bars { get; private set; }

    public ObservableCollection<ChartData> Populations { get; set; }

    public ObservableCollection<ChartData> Demo { get; set; }

   
    public MainViewModel()
    {

        Populations = new ObservableCollection<ChartData>()
            {
                new ChartData() { dataName="abc", dataValue = 123 },
                new ChartData() { dataName="def", dataValue = 421 },
                new ChartData() { dataName="ghi", dataValue = 342 },
                new ChartData() { dataName="jkl", dataValue = 213 },
            };


        Demo = new ObservableCollection<ChartData>()
            {
                new ChartData() { dataName="abc", dataValue = 123 },
                new ChartData() { dataName="def", dataValue = 421 },
                new ChartData() { dataName="ghi", dataValue = 342 },
                new ChartData() { dataName="jkl", dataValue = 213 },
            };


        Bars = new ObservableCollection<ChartSeries>();

        ChartSeries chartSerie = new ChartSeries();
        chartSerie.SeriesTitle = "Demo1";
        chartSerie.DisplayMember = "dataName";
        chartSerie.ValueMember = "dataValue";
        chartSerie.ItemsSource = Populations;
        Bars.Add(chartSerie);


        ChartSeries chartSerie1 = new ChartSeries();
        chartSerie1.SeriesTitle = "Demo2";
        chartSerie1.DisplayMember = "dataName";
        chartSerie1.ValueMember = "dataValue";
        chartSerie1.ItemsSource = Demo;
        Bars.Add(chartSerie1);

    }

}