@FozzieN ,   You can do exactly what you're trying to achieve using standard NiFi processors and a schema to describe your data structure. Please see attached a flow example that replicates what you are doing without the need for scripting. This flow uses the following schema, set as a parameter: { "type": "record", "name": "MyData", "fields": [ { "name": "source_timestamp", "type": "string" }, { "name": "signal", "type": "string" }, { "name": "value", "type": "string" }, { "name": "fecha_envio", "type": ["null", "string"], "default": null } ] }   Cheers, André ... View more