To ensure consistency of expectations and provide as descriptive a target as possible to develop against, where any fields in our service models hold no value we will favour emitting explicit null values over omitting these fields from the response entirely.

{
    "transactionId": "tx_0000B5HS9c5rd3zFzeLgOH",
    "amount": 50.00,
    "balance": null
}

over

{
    "transactionId": "tx_0000B5HS9c5rd3zFzeLgOH",
    "amount": 50.00
}