OpenBGPD set nexthop blackhole qualify question

Hi misc@ readers,

I have a question regarding the "set nexthop blackhole" nexthop
qualification in OpenBGPD 6.4 stable.

It looks like I have to add "nexthop qualify via default" in order for
the blackholed route to make it from the rib to the fib.

I understand this is standard behaviour for normal BGP nexthop
qualification, but is this mandatory/normal/expected for blackholed
prefixes too ?
I would have thought that since I am blackholing the prefix there's
nothing to qualify for anyway.

Thanks for your help and tremendous work !

Have a nice day !
Arnaud