how filling default values in prompt (current date)

hi

i am facing problem with filling with default values in Optional prompt (always current date )in webi

Prompt coming from Bex it is optional if i am not selecting any date Query will run as on date els user entry date .

if user not select any date in prompt dialog box fill with  current date .

EX: please find below attachment .

thanks in advance

Chandra

9840896759