Writing ADT not overwritten default values

[linuswagner]

I like to create metaData for my experiments. For that, I define an ADT and write it to json. Example:

data MetaData = metaData(
    datetime begin = now(),
    datetime end = now(),
    str usedModel = "",
    str commitIdMapperExperiments = getHeadId(|file:///home/linus/Documents/mapper-experiments|)
);

and then something like

md = metaData();
writeJSON(|some_path|, md, dateTimeAsInt=true, indent=4);

For some reason, the json file then only contains the string metaData. Only when I explicitly set the keyword attributes of the ADT, e.g.

md.begin = now();

the set attributes become part of the json.

I would expect that writing an ADT to a (json) file also includes the default values of the ADT, because (besides fitting my use-case), it cannot be guaranteed that default values remain unchanged between versions of Rascal. Since there is no version information in the file, this can lead to a loss of information.

[linuswagner]

Seems like the attributes don't appear in the argument in the Java code to begin with, so the problem might be how ADTs are handed over to Java