Extract elements

Good morning
I would like to ask for collaboration with a routine that I am trying to develop, and is to automatically generate finishes in the rooms, but I want to extract the walls of these nodes and I get false, as if it did not exist, I would like to know how I can do to extract the elements I need, thank you.

Replace the string node for the IsOfCategory node maybe, and hover over the inputs of that node, it will give you clues on what this animal feeds on.