无法从firebase回收器视图中的firebase实时数据库获取嵌套数据

{
  "users": {
    "userId1": {
      "name": "John",
      "age": 30,
      "address": {
        "city": "New York",
        "zip": "10001"
      }
    }
  }
}

{
  "rules": {
    ".read": "auth != null",
    ".write": "auth != null"
  }
}

import firebase from 'firebase/app';
import 'firebase/database';

// 初始化Firebase
const firebaseConfig = {
  apiKey: "YOUR_API_KEY",
  authDomain: "YOUR_AUTH_DOMAIN",
  databaseURL: "YOUR_DATABASE_URL",
  projectId: "YOUR_PROJECT_ID",
  storageBucket: "YOUR_STORAGE_BUCKET",
  messagingSenderId: "YOUR_MESSAGING_SENDER_ID",
  appId: "YOUR_APP_ID"
};

firebase.initializeApp(firebaseConfig);

// 读取嵌套数据
const userId = 'userId1';
const userRef = firebase.database().ref(`users/${userId}`);

userRef.once('value', (snapshot) => {
  const userData = snapshot.val();
  console.log(userData);
});