PATCH REST API to update a SharePoint List Item will put a blank value to a "Multiple lines of text" field with append changes option activated

Target SharePoint environment

SharePoint Online

What SharePoint development model, framework, SDK or API is this about?

SharePoint REST API

Developer environment

Windows

What browser(s) / client(s) have you tested

[ ] 💥 Internet Explorer
[ ] 💥 Microsoft Edge
[ ] 💥 Google Chrome
[ ] 💥 FireFox
[ ] 💥 Safari
[ ] mobile (iOS/iPadOS)
[ ] mobile (Android)
[X] not applicable
[ ] other (enter in the "Additional environment details" area below)

Additional environment details

Not applicable because the problem is related to how SharePoint treats the REST request.

Describe the bug / error

When a SharePoint list has "Item Version History" activated ("Create a version each time you edit an item in this list?" to "Yes"), and when there is a "Multiple lines of text" field with "Append Changes to Existing Text" set to "Yes", then if we use the REST API _api/web/lists/getbytitle('List')/items(Id) with the method PATCH to update an item, the "Multiple lines of text" field is set to a blank value.

Steps to reproduce

Create a SharePoint Online list and activate the versionning
Add a "Multiple lines of text" field and use "Yes" for "Append Changes to Existing Text"
Enter a new entry, either by doing it with SharePoint UI, or REST API, or SOAP Web Service, and put a value in the "Multiple Lines of Text" field

Retrieve the item using REST API

fetch("/sites/Demo/_api/web/lists/getbytitle('Demo')/items(1)", {
method:"GET",
headers:{
"X-RequestDigest": document.querySelector("#__REQUESTDIGEST").value,
"Accept": "application/json; odata=nometadata",
"Content-Type": "application/json; odata=nometadata"
}
})

It returns the below:

{
    "FileSystemObjectType": 0,
    "Id": 1,
    "ServerRedirectedEmbedUri": null,
    "ServerRedirectedEmbedUrl": "",
    "ContentTypeId": "0x0100755C42E31349534F9937768E0577E3C60042A0B5298D818C40B6247CEA99AF66A2",
    "Title": "Demo Entry 1",
    "OData__ColorTag": null,
    "ComplianceAssetId": null,
    "Multiple_x0020_lines_x0020_of_x0": "<div class=\"ExternalClass8D972C063C914EE0982E738777F81E71\"><div style=\"font-family&#58;Calibri, Arial, Helvetica, sans-serif;font-size&#58;11pt;color&#58;rgb(0, 0, 0);\">This is a demo test to show the bug.</div></div>",
    "ID": 1,
    "Modified": "2024-01-16T10:05:15Z",
    "Created": "2024-01-16T10:05:15Z",
    "AuthorId": 6,
    "EditorId": 6,
    "OData__UIVersionString": "1.0",
    "Attachments": false,
    "GUID": "a84fc243-7bc9-4b9d-8c12-efab66396a45"
}

Use REST API to update the "Title" field to a different value

fetch("/sites/Demo/_api/web/lists/getbytitle('Demo')/items(1)", {
method:"PATCH",
headers:{
"X-RequestDigest": document.querySelector("#__REQUESTDIGEST").value,
"Accept": "application/json; odata=nometadata",
"Content-Type": "application/json; odata=nometadata",
"IF-MATCH":"*"
},
body: JSON.stringify({"Title":"Hello World"})
})

Retrieve the item using REST API

fetch("/sites/Demo/_api/web/lists/getbytitle('Demo')/items(1)", {
method:"GET",
headers:{
"X-RequestDigest": document.querySelector("#__REQUESTDIGEST").value,
"Accept": "application/json; odata=nometadata",
"Content-Type": "application/json; odata=nometadata"
}
})

It returns the below:

{
    "FileSystemObjectType": 0,
    "Id": 2,
    "ServerRedirectedEmbedUri": null,
    "ServerRedirectedEmbedUrl": "",
    "ContentTypeId": "0x0100755C42E31349534F9937768E0577E3C60042A0B5298D818C40B6247CEA99AF66A2",
    "Title": "Hello World",
    "OData__ColorTag": null,
    "ComplianceAssetId": null,
    "Multiple_x0020_lines_x0020_of_x0": null,
    "ID": 2,
    "Modified": "2024-01-16T10:07:17Z",
    "Created": "2024-01-16T10:05:15Z",
    "AuthorId": 6,
    "EditorId": 6,
    "OData__UIVersionString": "2.0",
    "Attachments": false,
    "GUID": "a84fc243-7bc9-4b9d-8c12-efab66396a45"
}

Remark: Title has been updated to "Hello World", but Multiple_x0020_lines_x0020_of_x0 has also been updated to "null"!

Go to the item and check the "Version History":

As showed above, the "Multiple lines of text with History" field received an empty value when a different field has been updated by REST API, which will cause the field to now return a blank when trying to retrieve its value.

Current work arounds:

Use SOAP Web Services
Or we need first to retrieve the current value of the "Multiple lines of text with History", and then set it at the same time we update the other field...

Expected behavior

Updating a field in the item should not reset/put blank in another field.

SharePoint / sp-dev-docs