presto-main/src/main/java/io/prestosql/operator/scalar/JsonExtract.java/ObjectFieldJsonExtractor/extract
class ObjectFieldJsonExtractor:        @Override
        public T extract(JsonParser jsonParser)
                throws IOException
        {
            if (jsonParser.getCurrentToken() == START_OBJECT) {
                return processJsonObject(jsonParser);
            }

            if (jsonParser.getCurrentToken() == START_ARRAY) {
                return processJsonArray(jsonParser);
            }

            throw new JsonParseException(jsonParser, "Expected a JSON object or array");
        }