Errors reported while using bash-completion

Issue

• Using bash option nounset causes unbound variable errors while trying to use the bash auto-completion via the tab key.
• When the option nounset either set by set -u or set -o nounset commands while having bash-completion in place, any usage of tab key causes immediate errors reported:

  $ echo bash: !ref: unbound variable
bash: !ref: unbound variable
bash: words[i]: unbound variable