NiFi convert json to csv with optional attributes

[#1]

Hello,
I have a problem with converting json to csv.

I use ConvertRecord processor with attached JsonTreeReader and CSVRecordSetWriter.
The schema for both might look like this. Attributes in the json are optional.

{
"type": "record",
"name": "some_event",
"fields": [
{ "name": "date_time", "type": ["string","null"] },
{ "name": "id", "type": ["string","null"] },
{ "name": "is_success", "type": ["string","null"] },
{ "name": "username", "type": ["string","null"] },
{ "name": "username_type", "type": ["string","null"] }
]
}

for the input json like

{
"date_time": "2017-01-29T13:42:03.965Z",
"id": "20049015990001584400001"
"is_success": "TRUE",
}

where username and username_type is not set, the output does not correspond to my expectation

I get
2022-01-29T13:42:03.965Z|20049015990001584400001|true
instead of
2022-01-29T13:42:03.965Z|20049015990001584400001|true||
which should be the right format. Note the separator for null values at the end of the second record.

Do you have some hints, how to solve it? It should be sort of standard task.

The CSVRecordSetWriter is configured like this:

We use

Cloudera Flow Management (CFM) 2.0.4.3
1.11.4.2.0.4.3-1 built 01/06/2021 23:14:00 CET

Best regards
Jaro

[#2 · Accepted solution]

I have eventually solved the issue. The Writter property "Schema Access Strategy" was misconfigured. It must be set to "Use 'Schema Text' Property" to really apply the given schema .