Bash array expansion as command parameters

example

#!/usr/bin/env bash

((BASH_VERSINFO > 3)) || {
  echo 'Requires Bash 4+'
  exit
}

set -ux

echo foo 1 | tail "${tail_args[@]}"
# Result: Unbound variable, as expected

#-----
tail_args= # Empty variable
echo foo 2 | tail "${tail_args[@]}"
# Result: Errors, because this is equivalent to the following command:
echo foo 3 | tail ""

#-----
echo foo 4 | tail "${tail_args[@]:+"${tail_args[@]}"}"
# Result: Succeeds without passing the arguments, because this is equivalent to:
if [[ -n "${tail_args[*]}" ]]; then
  echo foo 5 | tail "${tail_args[@]}"
else
  echo foo 6 | tail
fi

tail_args=(-n 1)
echo foo 7 | tail "${tail_args[@]}"
echo foo 8 | tail "${tail_args[@]:+"${tail_args[@]}"}"
#----- No difference when the variable isn't empty