问颤动云场恢复Map<String，dynamic>错误

EN

The following assertion was thrown building StreamBuilder(dirty, state:
I/flutter (26287): _StreamBuilderBaseState>#d5638):

I/flutter (26287): type '_InternalLinkedHashMap' is not a subtype of type 'Map'

I/flutter (26287): where

I/flutter (26287):   _InternalLinkedHashMap is from dart:collection

I/flutter (26287):   Map is from dart:core

I/flutter (26287):   String is from dart:core

class Creator {
  const Creator({this.creatorId, this.name});

  Creator.fromDoc(DocumentSnapshot doc) : this.fromMap(doc.data);

  Creator.fromMap(Map map) :
    assert(map.containsKey('creatorId'),
    assert(map.containsKey('name'),
    this ( creatorId: map['creatorId'], name: map['name'] );

  /*

  ...

  */
}

return Scaffold(
  appBar: AppBar(title: new Text('Creators')),
  body: StreamBuilder(
    stream: CreatorRepo.getCreators().map>((creators) {
      return creators.documents.map((c) => Creator.fromSnapshot(c)).toList();
    }),
    builder: (BuildContext context, snapshot) {
      if ( snapshot.hasData ) {
        return ListView.builder(
          itemCount: snapshot.data.length,
          builder: (context, index) {
            final creator = snapshot.data[index];

            return ExpansionTile(
              title: Text(creator.name),
              children: [
                Text(creator.creatorId),
              ],
            );
          },
        );
      }

      return const CircularProgressIndicator();
    },
  ),
);

dependencies:
  flutter:
    sdk: flutter

  cloud_firestore: ^0.6.3
  firebase_messaging: ^0.2.4