Json Feeder - how do I reference the elements in session

I’m using a basic json feeder - it reads in the following json file:

[{
    "json": {
      "applicationType": "ED",
      "caseReferenceId": "00001379362",
      "contactDetails": {
        "contactTelephone": "00001379362"
        },
      "countryOfBirth": "GB"
    }
}]

I can reference the caseReferenceId using Gatling EL to retrieve the value in a standard http call: