error: Undefined name 'toPosts'.

[youyou-him]

I'm going to get the QuerySnapshot and change it to Post Model.

return FirebaseFirestore.instance
      .collection(COLLECTION_POSTS)
      .where(KEY_USERKEY, isEqualTo: userKey)
      .snapshots()
      .transform(toPosts);

I wrote it like this, and there's an error. In the error, it says that there is no to Posts, but even though I made it into a class, I can't get an imprint even if I try to make it's an error.

final toPosts =
  StreamTransformer<QuerySnapshot, List<PostModel>>.fromHandlers(
      handleData: (snapshot, sink) async {
        List<PostModel> posts = [];
        snapshot.docs.forEach((documentSnapshot) {
            posts.add(PostModel.fromSnapshot(documentSnapshot));
        });

What should I do

?