Hello,
When the -r, --no-run-if-empty option is combined with the -d, --delimiter or -0, --null options, the -r, --no-run-if-empty option does not take effect. The manual describes the intended behavior of the -r, --no-run-if-empty option: "If the standard input does not contain any nonblanks, do not run the command. Normally, the command is run once even if there is no input. This option is a GNU extension."
The following command correctly outputs nothing.
xargs --no-run-if-empty -I str echo str <<< ""
The following command incorrectly outputs 1 empty line.
xargs --no-run-if-empty --delimiter="\n" -I str echo str <<< ""
The following command incorrectly outputs 2 empty lines.
xargs --no-run-if-empty --null -I str echo str <<< ""
As a workaround according to
this Stack Overflow answer, the following commands output nothing when the input consists only of whitespace.
[[ $input = *[![:space:]]* ]] && xargs --delimiter="\n" -I str echo str <<< "$input"
[[ $input = *[![:space:]]* ]] || xargs --null -I str echo str <<< "$input"