title: How to execute functions on empty windows in Flink streaming?
body: <p>I wrote a Flink program that calculates the number of events per keyed window from a simple kafka stream. I works great, fast &amp; accurate. When the source stops, I would like to have <code>0</code> as result of the calculation on each window, but no result is sent. The function just does not execute. I assume this is because of the lazy operation behavior of Flink. </p>
  
  <p>Any recommendation?</p>