type '_SyncIterable<Widget>' is not a subtype of type 'List<Widget>' code example

Example 1: type '_Type' is not a subtype of type 'Widget'

wrong:
return Foo;
right:
return Foo();

Example 2: type 'List' is not a subtype of type 'List'

snapshot.data.documents.map<Widget>((document) {
  return new ListTile(
    title: new Text(document['name']),
    subtitle: new Text("Class"),
  );
}).toList()