Help with ads

Does anyone know the response format for ad events? I have a listener associated with the ad event but if I try checking event.response I get nil when it’s not an error. I’d like to be able to determine whether an ad is actually being served, so I can fill the space with a house ad if nothing came through.

local function adListener( event )  
  
 print ("ad event:" .. event.name)  
  
 if (event.isError) then  
 ads.hide()  
 adNetwork = "house"  
 end  
 --code for event.response okay but no ad fill  
end  

Thanks. [import]uid: 1560 topic_id: 23411 reply_id: 323411[/import]