mew, What version of NiFi are you using? We may have fixed the bug in newer versions but if you are using the latest, this is bug. We shouldn't infer CHOICE[STRING,RECORD] when the only entry is a RECORD.
Since you only have one top-level record in your FlowFile you can use JoltTransformJSON instead as a workaround. If you want JSON output then it's a solution and not a workaround :) The error here isn't about JOLT but about JoltTransformRecord using NiFi Records to apply the transformation to rather than the raw JSON (the latter is what JoltTransformJSON does). Regards, Matt
