modifying json with jsonbuilder for an integer type element in Groovy

Have the following JSON:

def jsonString = '{"studyDTO":{"studyId":191,"studyCode":"test_ispptest2"},"sites":[{"studyId":191,"siteRecid":16521,"siteId":"11001"}],"allSubjects":true,"states":null,"visits":[{"studyId":191,"visitSubmitName":"baseline","visitDisplayName":"Baseline","orderOfDisplay":10}],"modalities":null,"examDates":null,"series":null,"transferType":null,"sftpLocations":[],"dicomLocations":[],"fileSystemLocations":[],"rawFileSystemLocations":[],"customFolder":null,"folderStructure":null,"customFile":null,"fileStructure":null,"includePS":null}'

Want to update the value for "orderOfDisplay":10 with an integer from a data source dynamically.

def jsonConvert = new JsonSlurper();
def object = jsonConvert.parseText(jsonString);
def builder = new JsonBuilder(object)

builder.content.visits[0].orderOfDisplay = 23

[23 is only for example. I am running this for 10 times and every time the value is expected to change]

log.info(builder.toPrettyString());

similar to the post here, but in my case, I am trying to update an integer.

The error that I am getting after the update is,

{
    "studyDTO": {
        "studyId": 191,
        "studyCode": "test_ispptest2"
    },
    "sites": [
        {
            "studyId": 191,
            "siteRecid": 16521,
            "siteId": "11001"
        }
    ],
    "allSubjects": true,
    "states": null,
    "visits": [
        {
            "studyId": 191,
            "visitSubmitName": "cycle_1",
            "visitDisplayName": "Cycle 1",
            "orderOfDisplay": "23"
        }
    ],
    "modalities": null,
    "examDates": null,
    "series": null,
    "transferType": null,
    "sftpLocations": [
    ],
    "dicomLocations": [
    ],
    "fileSystemLocations": [
    ],
    "rawFileSystemLocations": [
    ],
    "customFolder": null,
    "folderStructure": null,
    "customFile": null,
    "fileStructure": null,
    "includePS": null
}

the value 23 is going in quotes