title: Datadog event trigger returns no data instead of 0
body: <p>I have created a event monitor( for example</p>
  
  <p><code>events('sources:rds event_source:db-instance').by('dbinstanceidentifier').rollup('count').last('1d') &gt;= 1</code>) </p>
  
  <p>but it returns "NO DATA" when there are no any events.</p>
  
  <p>How to make it return 0 when there are no any events?</p>