1362a0a55a
The [POSIX test manpage](https://pubs.opengroup.org/onlinepubs/9699919799/utilities/test.html) as well as the [fish test manpage](https://fishshell.com/docs/current/cmds/test.html#operators-for-text-strings) specify that `-z` will be "True if the length of string string is zero; otherwise, false." The `-n` was likely a mixup and not caught during testing of https://github.com/NixOS/nix/pull/8985 due to a lack of missing conflicting entries in `XDG_DATA_DIRS`.