bash_expansion_example.sh

#!/bin/bash
set -eux

flags=()

: "${flags[@]:-}"  # bad
: "${flags[@]}"    # good

flags=("thing w/ space" "other.thing")

: "${flags[@]:-}"  # good
: "${flags[@]}"    # good
: ${flags[@]}      # bad (obvs)

<<'EOF'
$ bash --version | head -n 1
GNU bash, version 5.0.17(1)-release (x86_64-pc-linux-gnu)

$ ./this_script.sh
+ flags=()
+ : ''
+ :
+ flags=("thing w/ space" "other.thing")
+ : 'thing w/ space' other.thing
+ : 'thing w/ space' other.thing
+ : thing w/ space other.thing
EOF