Elisp assertion for debugging

[Ypo]

I am trying to debug my init file: C-u prefix is not working.

I am using the elisp-bug-hunter package that has saved me many times in the past. But it doesn't work fine this time though, so it seems I need an “assertion elisp” to debug my init file.

What elisp _expression_ would return nil when C-u prefix works and non-nil when C-u prefix doesn't work?

I have tried

(eq (key-binding "C-u C-SPC") 'nil)

but it is probably a nonsense.

Best regards