How to set the Initial value of drilldown's token?

[SCSC]

I made drilldown from pie chart to scatter chart.

Pie chart :

<drilldown>
　<set token="BU">$row.BU$</set>
</drilldown>

search sentence of Scatter chart : 

<search>
 <query>
  index="indexA"
  | search BU=$BU$ 
  | eval XXX
 </query>
 <earliest>$field1.earliest$</earliest>
 <latest>$field1.latest$</latest>
</search>

Question : Can I set the  Initial or default value of this token?
I'm in trouble that scatter chart does not appear until you click something on pie chart.

[ITWhisperer · Accepted solution]

You could try adding a done handler to the search of the pie chart, and set the initial value of the token there.

[SCSC]

It was solved thanks to you.
Thank you very much !