presto-record-decoder/src/main/java/io/prestosql/decoder/json/DefaultJsonFieldDecoder.java/JsonValueProvider/getSlice
class JsonValueProvider:        @Override
        public Slice getSlice()
        {
            String textValue = value.isValueNode() ? value.asText() : value.toString();
            Slice slice = utf8Slice(textValue);
            if (isVarcharType(columnHandle.getType())) {
                slice = truncateToLength(slice, columnHandle.getType());
            }
            return slice;
        }