   // `toString` method on the map class.
    properties.add(DiagnosticsProperty&lt;Map&lt;Listenable, VoidCallback&gt;&gt;(
      'handles',
      handles,
      description: handles != null
        ? '${handles!.length} active client${ handles!.length == 1 ? "" : "s" }'
        : null,
      ifNull: 'no notifications ever received',
      showName: false,
    ));
  }
}
</code></pre>
<p>{@end-tool}</p>
<p>Used by <a href="../../gs_form_widget_form/GSForm/toDiagnosticsNode.html">toDiagnosticsNode</a> and <a