message: Handle null stdout/stderr in pretty.js
  Noticed while preparing this PR that you can wind up with `null` here if
  the process bombs out; let's make sure we avoid a crash in this case.
diff: @@ -32,8 +32,8 @@ const {stdout, stderr, status, error} = spawnSync(executable, [
  mode,
  glob,
  ]);
  -const out = stdout.toString().trim();
  -const err = stdout.toString().trim();
  +const out = (stdout || '').toString().trim();
  +const err = (stderr || '').toString().trim();
  function print(message) {
  if (message) {
  