`compose "${profile[@]}" up -d "${build[@]}"` aborts with "profile[@]:
unbound variable" on bash 4.3 and older, which treats expanding an EMPTY
array under `set -u` as unbound. DSM ships a newer bash, so this only
surfaced on QNAP. The ${arr[@]+"${arr[@]}"} form expands to nothing when
empty and is identical otherwise.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018SqJYt7jD7oUEkoY68sBZo