{
    "definitions": {
        "MySubObject": {
            "_id": "filled#",
            "properties": {
                "a": {
                    "type": "boolean"
                }
            },
            "required": [
                "a"
            ],
            "type": "object"
        }
    },
    "properties": {
        "empty": {
            "_id": "empty#"
        },
        "filled": {
            "$ref": "#/definitions/MySubObject"
        }
    },
    "required": [
        "empty",
        "filled"
    ],
    "type": "object"
}