@Override
        public byte[] getBytes(final String fieldName) {
            final String value = (String) source.get(getPhysicalColumnName(modelName, fieldName));
            if (StringUtil.isEmpty(value)) {
                return new byte[] {};
            }
            return Base64.getDecoder().decode(value);
        }
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