how to specify "useithreads" in a distroprefs

Hello there,

I've struggling to define distroprefs and include "useithreads" 
information for a perl that doesn't support it.

If I define it like this:

---
comment: Tests hang smoker
disabled: 1
match:
   distribution: ^PRBRENAN/Nasm-X86
   perlconfig:
     archname: i386-openbsd
     osname: openbsd
     useithreads: null

The distribution is skipped just fine, but then I start to get warning 
like this one:

validation of distropref 
'/home/goku/cpan-openbsd-smoker/prefs/PRBRENAN.Nasm-X86.yml'[0] against 
schema '/home/goku/perl5/lib/perl5/CPAN/Kwalify/distroprefs.yml' 
failed:   - [/match/perlconfig/useithreads] Non-valid data 'undef', 
expected text

I already tried to configure like this instead:

---
comment: Tests hang smoker
disabled: 1
match:
   distribution: ^PRBRENAN/Nasm-X86
   perlconfig:
     archname: i386-openbsd
     osname: openbsd
     no_useithreads: defined

But then the distribution is not skipped anymore.

I went through Kwalify documentation, but couldn't figure out where the 
CPAN distroprefs schema is define so I can figure out how to accomplish 
both things (skipping the distribution and not getting warnings).

Thanks in advance,

Alceu