@Override
        public void accept(final String fieldName, final byte[] fieldValue) {
            if (CollectionUtils.isEmpty(fieldValue)) {
                source.put(getPhysicalColumnName(modelName, fieldName), Const.EMPTY_STRING);
            } else {
                source.put(getPhysicalColumnName(modelName, fieldName), new String(Base64.getEncoder().encode(fieldValue)));
            }
        }
ElasticSearchConverter same as the HashMapConverter, but translate the column alias automatically.
oap-server/server-storage-plugin/storage-elasticsearch-plugin/src/main/java/org/apache/skywalking/oap/server/storage/plugin/elasticsearch/base/ElasticSearchConverter.java