Exists api has no effect on netsed field?

dsl:

 {
    "query": {
        "bool": {
            "filter": [
                {
                    "exists": {
                        "field": "LableToMember"
                    }
                }
            ]
        }
    }
}

doc:

{
    "LableToMember": [
        {
            "xxx": "xxx",
            "id": "1"
        }
    ],
    "field2":"xxx"
}  

LableToMember is a nested field and i can't get any doc.Exists api has no effect on netsed field?