Flutter 用于空值 FirebaseFirestore 的空值判断运算符

我想按日期对应用程序中的帖子进行排序，但当我使用orderby时，我得到了一个null check operator used on a null value错误.问题是，当我同时输入"where"和"orderby"时，就会出现问题.

我的代码如下:

StreamBuilder(
                  stream: FirebaseFirestore.instance
                      .collection('posts')
                      .where('uid', isEqualTo: widget.uid)
                      .orderBy(
                        'datePublished',
                        descending: true,
                      )
                      
                      .snapshots(),
                      
                  builder: (context, snapshot) {
                    if (snapshot.connectionState == ConnectionState.waiting) {
                      return const Center(
                        child: CircularProgressIndicator(),
                      );
                    }
                    return ListView.builder(
                        primary: false,
                        shrinkWrap: true,
                        itemCount: (snapshot.data! as dynamic).docs.length,
                        itemBuilder: (context, index) {
                          DocumentSnapshot snap =
                              (snapshot.data! as dynamic).docs[index];