presto-elasticsearch/src/main/java/io/prestosql/elasticsearch/decoders/SourceColumnDecoder.java/SourceColumnDecoder/decode
class SourceColumnDecoder:    @Override
    public void decode(SearchHit hit, Supplier<Object> getter, BlockBuilder output)
    {
        VARCHAR.writeSlice(output, Slices.utf8Slice(hit.getSourceAsString()));
    }