DataSeries.AddRange Error!!

[Jerry]

Hello,

When I use DataSeries.AddRange method,a exception occurs:

Object reference not set to an instance of an object.
at Telerik.Windows.Controls.Charting.DataSeries.InsertItem(Int32 index, DataPoint item) in c:\Builds\WPF_Scrum\HotFix_2010_Q2\Sources\Development\Controls\Chart\Chart\Data\DataSeries.cs:line 214

My code snap is followed:

DataSeries barSeries = new DataSeries();
var maxKey = features.Max(x => x.Key);
ObservableCollection<DataPoint> dataPoints=new ObservableCollection<DataPoint>();
Parallel.For(1, maxKey, i =>
             {
                 DataPoint dataPoint;
                 if (features.ContainsKey(i))
                 {
                      int xLabel = i*_mStatisticsStep;
                      dataPoint = new DataPoint(xLabel, features[i])
                                   {XCategory = xLabel.ToString()};
                  }
                  else
                  {
                       int xLabel = i*_mStatisticsStep;
                       dataPoint = new DataPoint(xLabel, 0)
                                   {XCategory = xLabel.ToString()};

                  }
                  dataPoints.Add(dataPoint);
                  });
barSeries.AddRange(dataPoints);

[Jerry]

Sorry for my question,It is my fault!
the collection contains null values!