title: Get results for an DateTime histogram aggregation even when there is no data
body: <p>Normally, when the data between two bounds of date, even if missing, is generated if 'extended_bounds' is used. Like in case, Date A -> Date B. Some dates between them have no data, but still can be generated in the result aggregation with their fields as NULL. </p>
  
  <p>But if I were to query something like Date X -> Date Y, where there is no data for either of the dates nor any intermediates, then the resultant bucket is []. Is there any way to generate result for such cases, even if all fields are marked as NULL or 0? </p>