code: static <K, V> void onSend(ProducerRecord<K, V> record, Span span) {
      setCommonTags(span);
      Tags.MESSAGE_BUS_DESTINATION.set(span, record.topic());
      if (record.partition() != null) {
        span.setTag("partition", record.partition());
      }
    }
docs: Called before record is sent by producer