Microsoft Academic API, Knowledge graph search — ReferenceIDs always empty

问题

I'm using the graph search method of the Microsoft Academic API to retrieve citation IDs and reference IDs for a paper. However, while retrieving citation IDs works, the reference IDs field is always empty, even for papers which should have linked references. For example, retrieving this publication through the API:

POST https://westus.api.cognitive.microsoft.com/academic/v1.0/graph/search?mode=json
Content-Type: application/json
Host: westus.api.cognitive.microsoft.com
Ocp-Apim-Subscription-Key: my-api-key

{  
    "path": "/paper",
    "paper": {  
        "select": [  
            "OriginalTitle",
            "CitationIDs",
            "ReferenceIDs"
        ],
        "type": "Paper",
        "id": [2059999322]
    }
}

yields this response (I shortened the CitationIDs list for the sake of legibility):

{
    "Results": [
        [
            {
                "CellID": 2059999322, 
                "CitationIDs": "[630584464,2053566310,2239657960,...]",  
                "OriginalTitle": "Biodistribution of colloidal gold nanoparticles after intravenous administration: Effect of particle size", 
                "ReferenceIDs": ""
            }
        ]
    ]
}

One thing I've noticed is that the graph schema provided here (at the bottom of the page) doesn't match the schema shown here (some of the attributes were renamed, e.g. NormalizedPaperTitle -> NormalizedTitle), so I thought the field was perhaps renamed to something else.

What is the correct query to get reference IDs through the API?