Recycle Bin is handled by the Windows Shell (since it's a special view that looks nothing like the real filenames on disk, and the only actions you can do within it are to restore or completely delete things).
Most Opus commands and scripting support isn't available in that folder, but also wouldn't normally be useful either (your case being an exception where it makes sense to need to query the selection count).
[Edit: Removed a section that I thought I'd already edited out. Info was only partially correct after testing things, and it wasn't important compared to the @ifsel thing.]
The only purpose of Set NOOP is to do nothing at all, which is occasionally useful. It always succeeds at doing nothing. 
After looking for a good way to do this, I also realised @ifsel won't work here in commands run via scripts, as none of those details are given to scripts when in Recycle Bin (at least currently).
Can you tell us more about what you're aiming to do? I can think of a few other approaches which should work, but am not sure which would be most suitable, and want to try them myself before sending you down the wrong path.