title: flutter map problem : final Completer<Null> _readyCompleter = Completer<Null>();
body: <p><strong>I am trying to build an app using flutter map plugin. But I got this error -</strong></p>
  <p><strong>Before this error I added this line -</strong></p>
  <pre class="lang-dart prettyprint-override"><code>Stream&lt;List&lt;DocumentSnapshot&gt;&gt; getDataCollectionByLocation({
      required GeoFirePoint center,
      required double radius,
      required String field,
    }) {
      Stream&lt;List&lt;DocumentSnapshot&gt;&gt; stream = _geo
          .collection(collectionRef: ref)
          .within(center: center, radius: radius, field: field);
      return stream;
    }
  </code></pre>
  <p><img src="https://i.stack.imgur.com/L8v0a.png" alt="" /></p>