What's the reasoning behind z & s returning nular for empty input?

[Sebastian Gniazdowski <sgniazdowski@xxxxxxxxx>]

Hi
arr=( "${(s:,:):-}" )
print -r ${#arr} ${(q)arr}
Output: 1 ''

arr=( "${(z):-}" )
print -r ${#arr} ${(q)arr}
Output: 1 ''

I guess the code is returning the nular (or something similar, as
nular is not defined in subst.c). I wonder why? Is the reason
historical? I always have to add exceptions to the code, especially
for (z). Maybe I'm not seeing some reason for this behavior?

-- 
Sebastian Gniazdowski
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