private void updateRecordConversionStats(Send completedSend) {
        // The underlying send might have accumulated statistics that need to be recorded. For example,
        // LazyDownConversionRecordsSend accumulates statistics related to the number of bytes down-converted, the amount
        // of temporary memory used for down-conversion, etc. Pull out any such statistics from the underlying send
        // and fold it up appropriately.
        if (completedSend instanceof LazyDownConversionRecordsSend) {
            if (recordConversionStats == null)
                recordConversionStats = new HashMap<>();
            LazyDownConversionRecordsSend lazyRecordsSend = (LazyDownConversionRecordsSend) completedSend;
            recordConversionStats.put(lazyRecordsSend.topicPartition(), lazyRecordsSend.recordConversionStats());
        }
    }
Get any statistics that were recorded as part of executing this {@link MultiRecordsSend}.
@return Records processing statistics (could be null if no statistics were collected)
clients/src/main/java/org/apache/kafka/common/record/MultiRecordsSend.java