title: How to pad empty values in date time aggregation
body: <p>When I do date histogram aggregation, there are no zero values if there is no data present in the inbetween dates. For example, after a date histogram aggregation, a typical result would be like below:</p>
  
  <pre><code>"buckets": [
    {
      "key_as_string": "2014-08-12T00:00:00.000Z",
      "key": 1409097600000,
      "doc_count": 2066
    },
    {
      "key_as_string": "2014-08-13T00:00:00.000Z",
      "key": 1409184000000,
      "doc_count": 7932
    },
    {
      "key_as_string": "2014-08-16T00:00:00.000Z",
      "key": 1409270400000,
      "doc_count": 9640
    }
  ]
  </code></pre>
  
  <p>Here as you can see, after the dates 12,13 the data is shown for 16 as in between dates has no data. I want the dates 14,15 to be shown with 0 as doc_count. Is it possible in elasticsearch?</p>