How do i get a blank field in the drop down box for a 'Approve' field?

[luvg]

I have a 'Approve' field in the user task tag in bpm20.xml
I have a 'Yes' and a 'No' value in the drop down list. These values are passed using <activiti:value>.  But initially i want a blank value in the drop down instead of auto populating it with 'Yes' or 'No'. How can i get the same?

[trademak]

Is it not possible to add an empty or "one space" field?

Best regards,