Filter empty object in odata

There is an oData service i want to call. We have an model that has an field Parent. The service tells me that the parent is an object with an iv that is an string inside. So we get the following model from the oData service:

{
"total": 0,
"items": [
    {
    "id": "string",
    "data": {
        "Title": {
            "en": "string",
            "nl": "string"
        },
        "Parent": {
            "iv": [
                "string"
            ]
        },
    }
]
}

Now when we get data back it looks like this:

{
    "total": 2,
    "items": [
        {
            "id": "6204c07d-1aef-4bd2-9646-e3ca36c63784",
            "data": {
                "Title": {
                    "en": "Test 1",
                    "nl": "Test 1"
                },
                "Parent": {
                    "iv": []
                },
            },
        },
        {
            "id": "bfd1b084-4166-4fec-9032-08047c8313d2",
            "data": {
                "Title": {
                    "en": "Test 2",
                    "nl": "Test 2"
                },
                "Parent": {
                    "iv": [
                        "6204c07d-1aef-4bd2-9646-e3ca36c63784"
                    ]
                },
            },
        },
}

Now i want to filter on all the items where parent is [] (so no parent selected). I've tried the following filters but all without success

data/Parent/iv eq [] | Returns 0 results
data/Parent/iv eq null | Returns 0 results
data/Parent eq null | Returns 0 results
length(data/Parent/iv) eq 0 | OData operation is not supported
not data/Parent/any() | Any/All may only be used following a collection.
not data/Parent/any() | Any/All may only be used following a collection.
data/Parent/iv/$count eq 0 | Server error

Solution

Found that for this case the following works:

empty(data/Parent/iv)