How to count the number of records of a JSON object flow file in NiFi?

I am calling an API which returns a JSON object as the body of the response as a flow file. I want to count the total records in the flow file.

I tried record processors like CalculateRecordStats needs a record reader and that in-turn needs a schema. But I don't have a schema. So Is there a better way to do it?

{
"result":[
    {
        "key1": "value1",
        "key2": "value2"
    },
    {
        "key1": "value1",
        "key2": "value2"
    }
]
}

This is the sample JSON the api response body returns. The records are the items of the list which is the value of the "result" key

In the above sample there are 2 records (2 items in the list). So that is what I want to calculate.

You can also answer here