How do I set my value_tok (click.value2) to "*" if the drilldown is on a chart legend?

I have the following drilldown:***mysearch***lineconnect When I click on a chart data point, then my value_tok token is set properly. The problem is when I click on a chart legend, the value_tok token is set to `$click.value2$`. How do I set my value_tok (ie click.value2) to `"*"` if the drilldown is on a chart legend?