Unsupported value - Simple Date format on Kibana

Elastic Stack Kibana
1

Hi all - I have a metric in my index that is in java.util.Date milliseconds, like this -> 1,547,659,500,000

I want to convert this to a date format like this -> January 16th 2019, 09:28:05.150

Can I do this with a painless script? If yes, how?

2

I managed to create a painless script

if (doc['StartTime'].value != null) {
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'");
simpleDateFormat.setTimeZone(TimeZone.getTimeZone("UTC"));
return simpleDateFormat.format(new Date(doc['StartTime'].value));
}

return 0;

and this is returning ""2019-01-10T11:57:00.000Z" but Kibana is still complaining with an "Unsupported script value" error. Any ideas why?