The following NoSuchMethodError was thrown building StreamBuilder<QuerySnapshot>

I tried to implement a Streambuilder to my application, but I get an error when I try my code. This is the error I get:

The following NoSuchMethodError was thrown building StreamBuilder(dirty, state: _StreamBuilderBaseState<QuerySnapshot, AsyncSnapshot>#be008):
The getter 'documents' was called on null.
Receiver: null
Tried calling: documents

And this is the code I tried:

 @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Test'),
      ),
      body: StreamBuilder(
        stream: Firestore.instance
            .collection('test')
            .document('OrRPMJJyPCThMYMi0mUl')
            .collection('test')
            .snapshots(),
        builder: (context, snapshot) {
          return ListView.builder(
            itemCount: snapshot.data.documents.length,
            itemBuilder: (context, index) {
              DocumentSnapshot reservation = snapshot.data.documents[index];
              return ListTile(
                title: Text(test['name']),
              );
            },
          );
        },
      ),
    );