message: Set undefined when isMultiple flag is empty
diff: @@ -24,6 +24,7 @@ const resolveHomeDir = (filepath) =>
  filepath && filepath.startsWith('~') ? path.join(process.env.HOME, filepath.slice(1)) : filepath;
  const trueIfSet = (value) => (value === '' ? true : value);
  +const undefinedIfEmpty = (array) => (array?.length ? array : undefined);
  export default async function getOptions({ argv, env, flags, log, packageJson }) {
  const fromCI = !!flags.ci || !!process.env.CI;
  @@ -35,8 +36,8 @@ export default async function getOptions({ argv, env, flags, log, packageJson })
  only: flags.only,
  onlyChanged: trueIfSet(flags.onlyChanged),
  - ignoreChanged: flags.ignoreChanged,
  - externals: flags.externals,
  + ignoreChanged: undefinedIfEmpty(flags.ignoreChanged),
  + externals: undefinedIfEmpty(flags.externals),
  list: flags.list,
  fromCI,
  skip: trueIfSet(flags.skip),
  