Updating an event where onlineMeeting exists will cause onlineMeeting to become null.

After updating the event with reference to the following document, the onlineMeeting that originally existed is now null.
https://docs.microsoft.com/en-us/graph/api/event-update?view=graph-rest-1.0&tabs=http

When we send the request, we specify the following

• "onlineMeetingProvider": "teamsForBusiness"
• "isOnlineMeeting":true

What I expected was that the onlineMeeting would not change.

Please let me know how to solve this problem.

※The following is the response to the GET of the calendar event to be updated. (Sensitive information is replaced with "xxx".)

Request: 

[GET]https://graph.microsoft.com/v1.0/me/events/${id}

Response:

{
    "@odata.context": "https://graph.microsoft.com/v1.0/$metadata#users('xxx')/events/$entity",
    "@odata.etag": "W/\"xxx\"",
    "id": "xxx",
    "createdDateTime": "2021-12-27T02:06:50.018009Z",
    "lastModifiedDateTime": "2021-12-27T02:06:53.3302716Z",
    "changeKey": "xxx",
    "categories": [],
    "transactionId": null,
    "originalStartTimeZone": "Asia/Tokyo",
    "originalEndTimeZone": "Asia/Tokyo",
    "iCalUId": "xxx",
    "reminderMinutesBeforeStart": 15,
    "isReminderOn": true,
    "hasAttachments": false,
    "subject": "xxx",
    "bodyPreview": "xxx",
    "importance": "normal",
    "sensitivity": "private",
    "isAllDay": false,
    "isCancelled": false,
    "isOrganizer": true,
    "responseRequested": true,
    "seriesMasterId": null,
    "showAs": "busy",
    "type": "singleInstance",
    "webLink": "https://outlook.office365.com/owa/?itemid=xxx&exvsurl=1&path=/calendar/item",
    "onlineMeetingUrl": null,
    "isOnlineMeeting": true,
    "onlineMeetingProvider": "teamsForBusiness",
    "allowNewTimeProposals": true,
    "isDraft": false,
    "hideAttendees": false,
    "recurrence": null,
    "responseStatus": {
        "response": "organizer",
        "time": "0001-01-01T00:00:00Z"
    },
    "body": {
        "contentType": "html",
        "content": "xxx"
    },
    "start": {
        "dateTime": "2021-12-31T10:00:00.0000000",
        "timeZone": "UTC"
    },
    "end": {
        "dateTime": "2021-12-31T11:00:00.0000000",
        "timeZone": "UTC"
    },
    "location": {
        "displayName": "",
        "locationType": "default",
        "uniqueIdType": "unknown",
        "address": {},
        "coordinates": {}
    },
    "locations": [],
    "attendees": [
        {
            "type": "required",
            "status": {
                "response": "none",
                "time": "1601-01-01T00:00:00Z"
            },
            "emailAddress": {
                "name": "xxx",
                "address": "Email address removed"
            }
        }
    ],
    "organizer": {
        "emailAddress": {
            "name": "xxx",
            "address": "Email address removed"
        }
    },
    "onlineMeeting": {
        "joinUrl": "https://teams.microsoft.com/l/meetup-join/xxx"
    }
}

※The following is an attempt to update the event. (Sensitive information is replaced with "xxx".)

Request: [PATCH]https://graph.microsoft.com/v1.0/me/events/${id}

{
    "subject": "xxx",
    "body": {
        "content": "xxx",
        "contentType": "Text"
    },
    "isAllDay": false,
    "isOrganizer": true,
    "start": {
        "dateTime": "2021-12-31T19:00:00.000",
        "timeZone": "Asia/Tokyo"
    },
    "end": {
        "dateTime": "2021-12-31T20:00:00.000",
        "timeZone": "Asia/Tokyo"
    },
    "organizer": {
        "emailAddress": {
            "name": "",
            "address": "Email address removed"
        }
    },
    "attendees": [
        {
            "status": {
                "response": "none"
            },
            "emailAddress": {
                "name": "",
                "address": "Email address removed"
            },
            "type": "required"
        }
    ],
    "location": {
        "displayName": ""
    },
    "sensitivity": "private",
    "isCancelled": "false",
    "onlineMeetingProvider": "teamsForBusiness",
    "isOnlineMeeting": true
}

Response: 

{
    "@odata.context": "https://graph.microsoft.com/v1.0/$metadata#users('xxx')/events/$entity",
    "@odata.etag": "W/\"xxxx\"",
    "id": "xxx",
    "createdDateTime": "2021-12-27T02:06:50.018009Z",
    "lastModifiedDateTime": "2021-12-27T02:10:07.7385468Z",
    "changeKey": "xxx",
    "categories": [],
    "transactionId": null,
    "originalStartTimeZone": "Asia/Tokyo",
    "originalEndTimeZone": "Asia/Tokyo",
    "iCalUId": "xxx",
    "reminderMinutesBeforeStart": 15,
    "isReminderOn": true,
    "hasAttachments": false,
    "subject": "xxx",
    "bodyPreview": "xxx",
    "importance": "normal",
    "sensitivity": "private",
    "isAllDay": false,
    "isCancelled": false,
    "isOrganizer": true,
    "responseRequested": true,
    "seriesMasterId": null,
    "showAs": "busy",
    "type": "singleInstance",
    "webLink": "https://outlook.office365.com/owa/?itemid=xxx",
    "onlineMeetingUrl": null,
    "isOnlineMeeting": false,
    "onlineMeetingProvider": "unknown",
    "allowNewTimeProposals": true,
    "isDraft": false,
    "hideAttendees": false,
    "recurrence": null,
    "onlineMeeting": null,
    "responseStatus": {
        "response": "organizer",
        "time": "0001-01-01T00:00:00Z"
    },
    "body": {
        "contentType": "html",
        "content": "xxx"
    },
    "start": {
        "dateTime": "2021-12-31T19:00:00.0000000",
        "timeZone": "Asia/Tokyo"
    },
    "end": {
        "dateTime": "2021-12-31T20:00:00.0000000",
        "timeZone": "Asia/Tokyo"
    },
    "location": {
        "displayName": "",
        "locationType": "default",
        "uniqueIdType": "unknown",
        "address": {},
        "coordinates": {}
    },
    "locations": [],
    "attendees": [
        {
            "type": "required",
            "status": {
                "response": "none",
                "time": "0001-01-01T00:00:00Z"
            },
            "emailAddress": {
                "name": "xxx",
                "address": "Email address removed"
            }
        }
    ],
    "organizer": {
        "emailAddress": {
            "name": "xxx",
            "address": "Email address removed"
        }
    }
}