cloudExport is exporting empty pdf when I use PieChart inside Report.view.php

the pdf / jpg export is not working with Charts.
MyReport.view.php
```
<h1>This is my first export using Chromeheadless.io</h1>
<?php
\koolreport\widgets\google\PieChart::create([
    'dataSource' => $this->dataStore("contacts_by_dependent_children"),
    'title' => 'Test'
]);
?>
```