code: protected int cleanInternal() {
          try (val expiredTickets = ticketRegistry.getTicketsStream().filter(Ticket::isExpired)) {
              val ticketsDeleted = expiredTickets
                  .mapToInt(this::cleanTicket)
                  .sum();
              LOGGER.info("[{}] expired tickets removed.", ticketsDeleted);
              return ticketsDeleted;
          }
      }
docs: Clean tickets.
  
  @return the int