Set empty list/hash on first access

[lizmat]

For some reason, the mainline is not run, so the 0 elems branches
would return an nqp::null, which gets upgraded to a Mu, which in
turn causes the exception of #4927

[vrurg]

If replaced with my %EMPTY-HASH; my @EMPTY-LIST then wouldn't it be equivalent but more tidy? Besides, no run-time would be involved whatsoever.

[lizmat]

I think the whole point was that it should be an NQP list/hash, not a HLL List / Map. In any case, I was changing the code as little as possible.

I tried your change, and it killed my Terminal session while doing a spectest.

Now trying to reproduce now

[niner]

Alternatively you could just move those variable declarations to the outer scope. That one's run for sure as it does all the add_method calls.

[lizmat]

I'm pretty sure I tried that. In any case, @vrurg's suggestion worked out.