Firebase数据库索引问题

Question

我的客户数据库是这样的：

{
    "customers": {
        "9115625853": {
            "address": "16-37-4/3, Innespeta, Rajahmundry 533101",
            "adhaar": "1111-2222-3333",
            "currentPackage": {
                "activation": "2016-11-22",
                "dataConsumed": 5905580032,
                "dataTotal": 21474836480,
                "expiry": "2016-12-22",
                "packageName": "5MB-20GB",
                "speedDown": "5 Mbps",
                "speedUp": "5 Mbps"
            },
            "email": "sureshk@gmail.com",
            "mobileno": "9115625853",
            "name": "Suresh Kumar P",
            "registered": "2016-11-22"
        },
        "7032906292": {
            "address": "46-17-24, Danavaipeta, Rajahmundry 533103",
            "adhaar": "5555-2342-3633",
            "currentPackage": {
                "activation": "2016-11-12",
                "dataConsumed": 18253611008,
                "dataTotal": 21474836480,
                "expiry": "2016-12-12",
                "packageName": "5MB-20GB",
                "speedDown": "5 Mbps",
                "speedUp": "5 Mbps"
            },
            "email": "lakshman@laurel.solutions",
            "mobileno": "7032906292",
            "name": "Lakshman Rao Pilaka",
            "registered": "2016-11-12"
        },
        "9165263347": {
            "address": "722 Junius Street, Grazierville, Indiana, 7463",
            "adhaar": "3935-1768-7293",
            "email": "mannray@biospan.com",
            "name": "Mann Ray",
            "phone": 9165263347,
            "registered": "2016-09-04"
        }
    }
}

我希望在将子项添加到未应用currentPackage的客户数据库（即添加9165263347 - Mann Ray之类的客户）时触发事件。

我写了这样的代码

firebase.database().ref('customers/')
  .orderByChild('currentPackage')
  .equalTo(null)
  .once('child_added')
  .then(function(snapshot) {

       // My Code

 });

我收到错误

  

未捕获（在承诺中）错误：没有为currentPackage定义索引（...）

我的Firebase规则如下

   {
    "rules": {
        ".read": true,
        ".write": true,
        "packages": {
            ".indexOn": "active"
        },
        "customers": {
            ".indexOn": "currentPackage"
        }
    }
}

我确信，规则定义中有错误，但不知怎的，我无法克服它。

请帮忙。

感谢。