Line chart with intermittent zero values - how to display?

[macaonghus]

I am charting the following data (for a lot of countries, and the data changes based on a pull down menu which selects the country).

Yr1 Yr2 Yr3 Yr4 Yr5
Country1 167 155 175 188 155
Country2 145 n.a. 150 140 166
Country3 142 154 n.a. 170 160


What I don't want is the line on the chart plummeting to zero when there is a "-", i.e. no value.

If I chart this instead:

Yr1 Yr2 Yr3 Yr4 Yr5
Country1 167 155 175 188 155
Country2 145 [.....] 150 140 166
Country3 142 154 [.....] 170 160

..., where [.....] means a blank cell, then the 145 does now show up at all.

What is a good way to resolve this?

Thank you!