How to convert String value to array in Apache Nifi

Question

all.

I have a query in a ExecuteSQLRecord processor which produces a JSON column in the result:

SELECT t.id, json_agg(json_build_object("value1", t.column1, "value2", t.column2)) AS "test" FROM table t GROUP BY t.id 

The processor uses a JSONRecordSetWriter to write the results. However, the processor returns a String from the database, which causes issues in further processing that expects a JSON value:

{
   ...
   "test": "[{\"value1\": \"column1value\", \"value2\": \"column2value\"}, ...]"
}

Is there a way of turning it to a proper JSON value, i.e., in this format:

{
   ...
   "test": [{"value1": "column1value", "value2": "column2value"}, ...]
}

without resorting to ReplaceText processors?

I have tried to replace the quotes in the SQL query, to use jsonb_agg() and jsonb_build_object(), and to use a QueryDatabaseTableRecord but none worked.

Thanks in advance.