I put about 10 data points in a pie chart to see their proportion. However, in an interval of time (about a week) some of the data points were down. In the meanwhile, the pie chart show the last value of these unavailable data (it is supposed to be 0) with existing data points in the same pie chart. Now the data points are restored back. How can I make the unavailable data points to zero as they should be in the pie chart ? Thanks !