OWASP ZAP reported “alert(1);” XSS vulnerability, but no popup showed up

OWASP ZAP reported “alert(1);” XSS vulnerability, but we could not get pop up in browser.

The html surrounding the injected attack is:

<script type="text/javascript">
  DataSet.FilterBuilder.QueryValuesDictionary['57_ctl00'] = ;alert(1);;
</script>