我正在努力解决这两个错误。
错误：无法无条件访问属性"docs"，因为接收器可以为"null"。（[church_app] lib\Screens\DevotionalList. dart：23处的unchecked_use_of_nullable_value）
错误：参数'devotional'的值不能为'null'，因为其类型不同，但隐式默认值为'null'。（[church_app] lib\Screens\DevotionalList. dart：39处缺少参数的默认值）

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';

class DevotionalList extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return StreamBuilder<QuerySnapshot>(
      stream: FirebaseFirestore.instance.collection('devotionals').snapshots(),
      builder: (context, snapshot) {
        if (snapshot.hasError) {
          return Center(
            child: Text('Error: ${snapshot.error}'),
          );
        }

        if (!snapshot.hasData) {
          return Center(
            child: CircularProgressIndicator(),
          );
        }

        // Use the .docs property to access the list of documents.
        List<DocumentSnapshot> documents = snapshot.data.docs;
        return ListView.builder(
          itemCount: documents.length,
          itemBuilder: (context, index) {
            DocumentSnapshot devotional = documents[index];
            return DevotionalTile(devotional: devotional);
          },
        );
      },
    );
  }
}

class DevotionalTile extends StatelessWidget {
  final DocumentSnapshot devotional;

  DevotionalTile({this.devotional});

  @override
  Widget build(BuildContext context) {
    if (devotional == null) {
      return Container();
    }

    return ExpansionTile(
      title: Text(devotional['title']),
      subtitle: Text('By ${devotional['author']}'),
      children: <Widget>[
        Padding(
          padding: const EdgeInsets.all(8.0),
          child: Text(devotional['body']),
        ),
      ],
    );
  }
}

如有任何帮助，不胜感激。
尝试添加空异常，但仍然遇到相同的错误。