Until the feature becomes available use the following workaround:

MyPivotGridChartDataProvider chartProvider = new MyPivotGridChartDataProvider(this.radPivotGrid1.PivotGridElement);
this.radPivotGrid1.ChartDataProvider = chartProvider;
this.radChartView1.DataSource = this.radPivotGrid1;
this.radChartView1.ShowLegend = true;
this.radPivotGrid1.ChartDataProvider.SeriesAxis = Telerik.Pivot.Core.PivotAxis.Rows;
this.radPivotGrid1.ChartDataProvider.GeneratedSeriesType = Telerik.WinControls.UI.GeneratedSeriesType.Line;

public class MyPivotGridChartDataProvider : PivotGridChartDataProvider
{
    public MyPivotGridChartDataProvider(RadPivotGridElement pivotGridElement)
        : base(pivotGridElement) { }

    public override void UpdateChartData()
    {
        base.UpdateChartData();

        foreach (ChartSeries series in this.ChartView.Series)
        {
            CartesianSeries cartesianSeries = series as CartesianSeries;
            if (cartesianSeries == null)
            {
                continue;
            }

            cartesianSeries.PointSize = new SizeF(7, 7);

            BindingList<PivotChartModelPoint> newData = new BindingList<PivotChartModelPoint>();
            BindingList<PivotDataPoint> points = cartesianSeries.DataSource as BindingList<PivotDataPoint>;

            foreach (PivotDataPoint point in points)
            {
                PivotChartModelPoint current = new PivotChartModelPoint() { Group = point.PivotGroup };
                if (point.Value != 0)
                {
                    current.Value = point.Value;
                }
                else
                {
                    current.Value = null;
                }

                newData.Add(current);
            }

            cartesianSeries.DataSource = null;

            cartesianSeries.CategoryMember = "Group";
            cartesianSeries.ValueMember = "Value";
            cartesianSeries.DataSource = newData;
        }
    }
}

public class PivotChartModelPoint
{
    public string Group{ get; set; }

    public double? Value { get; set; }
}