Null entry appearing in array output from dataweave

Question

I'm using Anypoint Studio 7.3 and Mule 4.2.

I'm transforming a payload but I'm getting a random null at the end of the new array and cannot work out why it is appearing when I process this record.

Can anyone see why this problem is occurring?

Dataweave Code

%dw 2.0
output application/json
---
payload.records flatMap
    ((record, index) ->
        records.customers flatMap ((customer, index) ->
            customers.transactions flatMap ((transaction, index) ->
                transaction.prices filter (!isEmpty($)) map ((price, index) ->
                {
                    recordId: record.recordId,
                    customerId: customer.customerId,
                    transactionId: transaction.sessionId,
                    name: customer.name,
                    value: price.value
                })
            )
        )
    )

Input JSON

{
    "records": [
        {
            "recordId": "f4f80bc7",
            "customers": [
                {
                    "customerId": "a1f773b8",
                    "name": "J Smith",
                    "transactions": [
                        {
                            "transactionId": "f610bac1"
                            "prices": [
                                {
                                    "value": 580
                                },
                                {
                                    "value": 8403,
                                },
                                {
                                    "value": 8983
                                }
                            ]
                        }
                    ]
                }
            ]
        }
    ]
}

Output JSON with random null

[
  {
    "recordId": "f4f80bc7",
    "customerId": "a1f773b8",
    "transationId": "f610bac1",
    "name": "J Smith",
    "value": 580
  },
  {
    "recordId": "f4f80bc7",
    "customerId": "a1f773b8",
    "transationId": "f610bac1",
    "name": "J Smith",
    "value": 8403
  },
  {
    "recordId": "f4f80bc7",
    "customerId": "a1f773b8",
    "transationId": "f610bac1",
    "name": "J Smith",
    "value": 8983
  },
  null
]

Thanks for any help

Answer 1

You can skip null elements in your array with the writer property skipNullOn.

output application/json skipNullOn="arrays".

Just a comment here: With your DW script and input, I couldn't reproduce your output with the null element in Mule 4.2