无法从嵌套对象firestore streambuilder列表视图中检索数据

{
  "users": [
    {
      "name": "John",
      "age": 25,
      "address": {
        "city": "New York",
        "country": "USA"
      }
    },
    {
      "name": "Jane",
      "age": 30,
      "address": {
        "city": "London",
        "country": "UK"
      }
    }
  ]
}

StreamBuilder(
  stream: Firestore.instance.collection('users').snapshots(),
  builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
    if (snapshot.hasError) {
      return Text('Error: ${snapshot.error}');
    }

    if (snapshot.connectionState == ConnectionState.waiting) {
      return Text('Loading...');
    }

    if (!snapshot.hasData) {
      return Text('No data found.');
    }

    return ListView.builder(
      itemCount: snapshot.data.documents.length,
      itemBuilder: (BuildContext context, int index) {
        DocumentSnapshot document = snapshot.data.documents[index];
        String name = document.data['name'];
        int age = document.data['age'];
        String city = document.data['address']['city'];
        String country = document.data['address']['country'];

        return ListTile(
          title: Text(name),
          subtitle: Text('Age: $age, Address: $city, $country'),
        );
      },
    );
  },
)