title: error trying to get a document from firebase using UID, Flutter app
body: <p>Im getting 2 error in my code trying to get a document from a Firebase collection <code>/users</code> using UID,
  base on this document <a href="https://firebase.flutter.dev/docs/firestore/usage/#one-time-read" rel="nofollow noreferrer">FlutterFire</a></p>
  <p><strong>First one =&gt;</strong> error: Too many positional arguments: 0 expected, but 1 found. (extra_positional_arguments_could_be_named at [calfran_app] lib/pages/home.dart:49)`</p>
  <p><strong>Second one</strong> =&gt; error: Undefined name 'users'. (undefined_identifier at [calfran_app] lib/pages/home.dart:37)</p>
  <pre><code>class _HomeState extends State&lt;Home&gt; {
  
    Widget build(BuildContext context) {
      Stream documentStream = FirebaseFirestore.instance.collection('users').doc('user.uid').snapshots();
  
  
      int _currentIndex = 0;
  
      final tabs = [
  
        //TAB DE MANUAIS
        Center(
            child: (Scaffold(
  
                body:  StreamBuilder&lt;QuerySnapshot&gt;(
                    stream: users.snapshots(), 
                     builder: (BuildContext context, AsyncSnapshot&lt;QuerySnapshot&gt; snapshot){
                      if (snapshot.hasError) {
                        return Text('Something went wrong');
                      }
  
                      if (snapshot.connectionState == ConnectionState.waiting) {
                        return Text(&quot;Loading&quot;);
                      }
  
                      return Container(
                        padding: EdgeInsets.all(16),
                        child: ListView(
                         snapshot.data.documents.map((DocumentSnapshot document) {
  
  
                              var dio = Dio();
  
                              return Card(
                                color: Colors.grey[250],
                                child: Container(
                                  padding: EdgeInsets.all(10),
                                  child: Column(
                                    crossAxisAlignment: CrossAxisAlignment.start,
  
                                    children: &lt;Widget&gt;[
  
                                      new Image.asset(
                                        'Images/pdflogo.png', width: 32,
                                      ),
                                      Center(
                                        child: Text(
                                          (document.data()['nome'].toString()),
                                          maxLines: 1,
                                          overflow: TextOverflow.ellipsis,
                                          style: TextStyle(fontSize: 16),
  
                                        ),
                                      ),
  
                                      ButtonBar(
                                        children: &lt;Widget&gt;[
  
                                          FlatButton(
                                              child: const Text(
                                                  'Compartilhar / Download'),
                                              onPressed: () async {
                                                var request = await HttpClient()
                                                    .getUrl(Uri.parse(
                                                    document.data()['documento']));
                                                var response = await request
                                                    .close();
                                                Uint8List bytes = await consolidateHttpClientResponseBytes(
                                                    response);
                                                await Share.file(
                                                    'ESYS AMLOG',
                                                    'Manual.pdf',
                                                    bytes,
                                                    'image/jpg');
                                              }),
  
  
                                        ],
                                      ),
                                    ],
                                  ),
                                ),
                              );
                            }),
                      ));
                    })))),
  </code></pre>