dataRecord.get / calling an unmatched pattern

i've got the following problem.
I am scraping listings. They all have a different number of images.

The problem is that if a listing has 4 images, and a previous one has 5,
the session variable from the previous listing is also used for the next.

The method is [i]apply pattern after each pattern application[/i].

So i am trying to do this in a script:

if(dataRecord.get( "image5" ) == "" )
{
session.setVariable( "image5", null );
}
// call the Save scrape
session.scrapeFile( "Save_images" );

But what ever i try, nothing seems to work. The log indicates:
Scrape_images: Extracting data for pattern "image5"
Scrape_images: The pattern did not find any matches.

But: Scrape_images: POST data: still posts the image5
from the previous listing.

Anyone can help?