modalpopup issue on button click

[Saadettin]

Hi. I have a problem with modalpopup. I try to do thing like this. I set modalPopup.OpenerElementID :

modalPopup.OpenerElementID = btngetReport.ClientID;

This code works. On button click event, I control a value is null or not. If value is null, modalpopup is not hown, else modalpopup will be shown. But I can not do this.

I try a code on button click like below:

......
.....
if(val==null)
modalPopup.Visible = false;

How can I do this? Thanks in advance..