The GZIP variable makes set -u fail

We define GZIP="--no-name ${GZIP}, instead we should do GZIP="--no-name ${GZIP:-}.

We also have #40002 about removing this variable.

However, it's a bit complex. The way to do it is -I 'gzip --no-names', but we prefer using -a.

Another idea is to just stop using it, since we ship gz archives only for the expert bundle (and for that we could be explicit).

For now, I'd just apply the fix, and leave #40002 for another time.