title: Error in loading data from cloud firestore
body: <pre><code>body: StreamBuilder(
        stream: Firestore.instance.collection('students').document(_userId).snapshots(),
        builder: (context,snapshot) {
          return  Container(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.start,
              children: &lt;Widget&gt;[
                SizedBox(
                  height: 20.0,
                ),
                Row(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: &lt;Widget&gt;[
                    Padding(
                      padding: const EdgeInsets.only(left:20.0),
                      child: Align(
                        alignment: Alignment.centerRight,
                        child: CircleAvatar(
                          radius: 100,
                         backgroundColor: Colors.white,
                          child: ClipOval(
                            child: new SizedBox(
                              width: 180.0,
                              height: 180.0,
                              child: (_image!=null)?Image.file(
                              _image,
                              fit: BoxFit.fill,
                            ):
                            Image.network(""),
                            ),
                          ),
                        ),
                      ),
                    ),
                    Padding(
                      padding: EdgeInsets.only(top: 60.0),
                      child: IconButton(
                        icon: Icon(
                          Icons.camera,
                          size: 30.0,
                        ),
                        onPressed: () {
                          getImage();
                        },
                      ),
                    ),
                  ],
                ),
                SizedBox(
                  height: 20.0,
                ),
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                  children: &lt;Widget&gt;[
                    Padding(
                      padding: const EdgeInsets.only(left:40.0),
                      child: Align(
                        alignment: Alignment.center,
                        child: Container(
                          child: Column(
                            children: &lt;Widget&gt;[
                              Align(
                                alignment: Alignment.center,
                                child: Text('Student Name',
                                    style: TextStyle(
                                        color: Colors.white, fontSize: 20.0)),
                              ),
                              Align(
                                alignment: Alignment.center,
                                child: Text(snapshot.data['first_name'],
                                    style: TextStyle(
                                        color: Colors.black,
                                        fontSize: 18.0,
                                        )),
                              ),
                            ],
                          ),
                        ),
                      ),
                    ),
  </code></pre>
  
  <p>i want to display student name from cloud firestore but it gives an error upon first loading but after hotreload the app works correctly.
  here is my student id retrieving function </p>
  
  <pre><code>FirebaseAuth.instance.currentUser().then((user) {
    _userId = user.uid;
  });
  </code></pre>
  
  <p>i am using this id for retrieving a particular student details but it give error upon first loading the error are <a href="https://i.stack.imgur.com/a70h4.png" rel="nofollow noreferrer">enter image description here</a> 
  The database snap are <a href="https://i.stack.imgur.com/6jm4K.png" rel="nofollow noreferrer">enter image description here</a></p>