title: How to rewrite this in dart to avoid the cast error
body: <p>I have this piece of code, I want to return a stream of documentshapshots.</p>
  <pre><code>/* Get Firestore products docs
   */
    Stream&lt;List&lt;DocumentSnapshot&gt;&gt; fetchFirstProductListStream() {
      
      ....
     return  getFirestoreUserStream(loggedInUser.uid).map((UserModel rad) =&gt; 
      (geo
            .collection(collectionRef: collectionReference)
            .within(center: center, radius: rad.radius, field: field)) as List&lt;DocumentSnapshot&gt;
      );
  }
  </code></pre>
  <p>I do get the following error as I try to cast the return value to List.</p>
  <pre><code>&gt; [VERBOSE-2:ui_dart_state.cc(186)] Unhandled Exception: type
  &gt; '_AsBroadcastStream&lt;List&lt;DocumentSnapshot&gt;&gt;' is not a subtype of type &gt; &gt; 'List&lt;DocumentSnapshot&gt;'
  </code></pre>