Graph Search API - retrieve site columns values

Question

Im successfully using graph search API to retrieve driveItems & listItems for specified query. Unfortunately I am unable to attach to returned data site column values.
Ive tired to include them by specifying fields property in request =>

            "fields": [ "MySiteColumn" ],

or separately setting expand parameter =>

"expand": [ "fields(select=MySiteColumn)"  ],

but still site column value is not being included, mine search request looks like

{
    "requests": [
        {
            "entityTypes": [ "driveItem","listItem" ],
            "query": { "queryString": "dlcDocId:BCUAT-1449193218-16293" }
        }
    ]
}

I would like to know if it is possible to retrieve SP site column value in search result - and if so - then how I can do this.