Removing session variables in latest version

I recently upgraded my version of SS and a key feature no longer works as it used to. To summarise, i used to essentially reset the session variables to blank by overwriting a session variable with something that was always null. On the recent update it's no longer possible to remove the session variables as i used to as these null variables are now ignored.

The best way to describe this is through an example:

Category -> Subcategory -> Child category.

When scraping a site with the structure as above I used to grab the names of the category, subcategory and children, which is great until you get back to the category level where the child name and subcategory name session variables are still active. I used to reset the subcat/child name to null by scraping somethnig that was blank. THis no longer works so when the varialbes are written out the subcat and child data is written out as well.

I hope this explains what i'm trying to do.

What can i do now to remove the session variables or reset them?

Richard