code: private void incrementRejectedMessages(Verb verb)
      {
          DroppedMessageMetrics metrics = droppedMessages.get(verb);
          if (metrics == null)
          {
              metrics = new DroppedMessageMetrics(verb);
              droppedMessages.put(verb, metrics);
          }
          metrics.dropped.mark();
      }
docs: Same as incrementDroppedMessages(), but allows non-droppable verbs. Called for IMessageSink-caused message drops.