When is it good to use #+implementation ?

I have checked that the Spartns library works with Poplog. However,
some tests fail because I use (make-hash-table :size 0), which
Poplog complains about[0].

I have already reported this on comp.lang.pop, but I was wondering
when it is considered OK to use #+ to include or exclude code for
different implementations.

All tests pass if I use
(make-hash-table :size #+poplog (max 1 size) #-poplog 0)


I don't want to use :size 1 because this argument is also
used for other representations (liek compressed vectors), and
I don't want to allocate lots of vectors of size 1...

Thanks,
J.

[0] CLtL requires the argument to be a "non-negative integer", which
in my understanding includes zero. :-)

.