title: return a list from a future in flutter
body: <p>Hi i'm new to flutter and asynchronous programming. i need to do something like this: </p>
  
  <pre><code>List&lt;Widget&gt; usersProfiles = [];
        getUsers('DcofOiHWcjbjD0i18miW').then((user) {
          user.forEach((u) {
            usersProfiles.add(new ListTile(
              leading: CircleAvatar(
                backgroundImage: AssetImage(u.profilePicture),
              ),
              trailing: u.icon,
              title: new Text(u.name),
              onTap: () {
                Navigator.push(context,
                    new MaterialPageRoute(builder: (context) =&gt; new Home()));
              },
            ));
          });
        });
  </code></pre>
  
  <p>but <code>usersProfiles</code> returns <code>null</code></p>
  
  <p>I'll be very greatful</p>