Air not able to be made into a variable?

[NotSlapdash]

I've tried setting a variable's material to air so I could remove air from a list but air just remains, I cannot figure it out and I'm pretty sure I did this a year or so ago but I can't remember what I did. Also weren't there tickets on the discord for these questions before? Maybe I missed something.

Here is the DFOnline link: DFOnlineCode

I found the help area in discord, I wasn't verified. Here is a solution that worked for me: Solution