{
    "locals": {
        "instances":{
            "a": 1
        }
    },
    "provider": {
        "null":{
            "alias": "blah",
            "for_each": "${local.instances}"
        }
    },
    "resource": {
        "null_resource": {
            "test": {
                "for_each": "${local.instances}",
                "provider": "null.blah[each.key]"
            }
        }
    }
}
