message: API: Fix addWhitelistedUserToCourses findIndex < 0
diff: @@ -289,7 +289,7 @@ export class AuthController {
  await Promise.all(
  courses.map(async (course) => {
  - if (course.students.findIndex(u => user._id === u._id < 0)
  + if (course.students.findIndex(u => user._id === u._id) < 0
  && course.whitelist.find(w =>
  w.uid === user.uid)
  ) {
  