# File lib/messenger/messenger.rb, line 621
    def settle(tracker)
      raise TypeError.new("invalid tracker: #{tracker}") unless valid_tracker?(tracker)
      if tracker.nil? then
        tracker = self.incoming_tracker
        flag = Cproton::PN_CUMULATIVE
      else
        flag = 0
      end
      Cproton.pn_messenger_settle(@impl, tracker.impl, flag)
    end