graphClient.Me.GetAsync() / graphClient.Users.GetAsync() can't get AdditonalData from Type "#Collection(String)"

Describe the bug

Hello,
I'm trying to retrieve some Entra ID directory extensions from users using the Graph SDK. It works with normal strings, but if I have an array as data type, it just displays an empty object.

If I use the following code block:

var me = await graphClient.me.GetAsync(requestConfiguration =>
{
    requestConfiguration.QueryParameters.Select =
        new string[] { "Id", "extension_c4eaf7e0c68a468c8a93aa91dc1cdf8e_roomNumber", "extension_c4eaf7e0c68a468c8a93aa91dc1cdf8e_info" };
});

I receive:

{
    "AdditionalData": {
        "@odata.context": "https://graph.microsoft.com/v1.0/$metadata#users(id,extension_c4eaxxxxxxxxxxxxxxxxaa91dc1cdf8e_roomNumber,extension_c4eaxxxxxxxxxxxxxxxxaa91dc1cdf8e_info)/$entity",
        "extension_c4eaxxxxxxxxxxxxxxxxaa91dc1cdf8e_roomNumber@odata.type": "#Collection(String)",
        "extension_c4eaxxxxxxxxxxxxxxxxaa91dc1cdf8e_roomNumber": {},
        "extension_c4eaxxxxxxxxxxxxxxxxaa91dc1cdf8e_info": "11 IT 04 Anwendungsdienste - Kollaboration"
    },
    "BackingStore": {
        "InitializationCompleted": true,
        "ReturnOnlyChangedValues": false
    },
    "Id": "c959de31-XXXX-XXXX-XXXX-276f63552369",
    "OdataType": "#microsoft.graph.user"
}

Expected behavior

I expect all the values to be displayed as if I go directly to the HTTP API.
URL: https://graph.microsoft.com/v1.0/me?$select=id,extension_c4eaxxxxxxxxxxxxxxxxaa91dc1cdf8e_roomNumber,extension_c4eaxxxxxxxxxxxxxxxxaa91dc1cdf8e_info

Output:

{
    "@odata.context": "https://graph.microsoft.com/v1.0/$metadata#users(id,extension_c4eaxxxxxxxxxxxxxxxxaa91dc1cdf8e_roomNumber,extension_c4eaxxxxxxxxxxxxxxxxaa91dc1cdf8e_info)/$entity",
    "id": "c959de31-XXXX-XXXX-XXXX-276f63552369",
    "extension_c4eaxxxxxxxxxxxxxxxxaa91dc1cdf8e_roomNumber@odata.type": "#Collection(String)",
    "extension_c4eaxxxxxxxxxxxxxxxxaa91dc1cdf8e_roomNumber": [
        "E.6.160"
    ],
    "extension_c4eaxxxxxxxxxxxxxxxxaa91dc1cdf8e_info": "11 IT 04 Anwendungsdienste - Kollaboration"
}

How to reproduce

var graphClient = new GraphServiceClient(credential, scopes);
var me = await graphClient.Me.GetAsync(requestConfiguration => {
    requestConfiguration.QueryParameters.Select =  new string[] { "Id", "extension_c4eaxxxxxxxxxxxxxxxxaa91dc1cdf8e_roomNumber", "extension_c4eaxxxxxxxxxxxxxxxxaa91dc1cdf8e_info" };
});
Console.WriteLine(JsonSerializer.Serialize(me!));

SDK Version

5.78.0

Latest version known to work for scenario above?

5.46.0

Known Workarounds

No response

Debug output

No response

Configuration

-OS: Windows 11
-Architecture: x64
-IDE: Visual Studio 2022 17.14.0

Other information

No response

Start with the GraphServiceClient.Me.GetAsync reproduction in the issue and compare behavior between SDK versions 5.46.0 and 5.78.0. Trace how the selected extension field marked #Collection(String) is deserialized into AdditionalData. Done means the SDK preserves the returned string array instead of producing an empty object.