Line graph based on cross table - Do not show null values

[OlafOdersky]

We display a line graph based on a cross table (lines = different text values / rows = months 1-12)

Sample:
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Product a 1,5 1,7 1,9 0 0 0 0 0 0 0 0 0
Product b 0,5 0,9 1,3 0 0 0 0 0 0 0 0 0
Product c 1,9 2,1 2,5 0 0 0 0 0 0 0 0 0

The problem is based on the month with no values. In this example there exists no data for the month Apr - Dec. So the cross table shows this value with zero. The line chart based on this cross table shows the values for Jan - Mar correctly. From Mar the lines goes down to zero. This is not the effect we would like to show. Exactly there have to be no lines for the months that have no values. Is it possible to hide the lines for non existing data? The correct chart should only show lines from Jan to Mar and should stop there. The months Apr to Dec should be shown but with no values/lines.

Any tips?

Thanks a lot
Olaf