Fix(bash<4.4): Empty arrays shall not be "unset"

Prior to Bash 4.4 `set -u` treats empty arrays as "unset"
and terminates the process; see:
https://gist.github.com/dimo414/2fb052d230654cc0c25e9e41a9651ebe

Change-Id: I92ca59037ba322e10fed9ec221aa4e1a0884ea8f