for comprehension problem

def findOne(id: BSONObjectID): Future[Option[reactive.models.User]] = {
    val query = BSONDocument("_id" -> id)
    val cursor = users.find(query).cursor[BSONDocument]

    for {
      // get a future option of user
      maybeUser <- cursor.headOption
      // if there is some user, return a future of result with the user
      result <- maybeUser.map { doc =>
        Option(userReader.read(doc))
      }.get

    } yield result
  }