This is basically follow up of issue CompositeAgg Histograms - fill empty interval gaps like normal histogramAggregation
It would be nice if DateHistogram under Composite agg behaves more like plain DateHistogram.
IDK if this is bug or feature, but it would be handy when Composite DateHistogram supports
- empty buckets
- returning key not only as timestamp but key_as_string too.
The motivation for this is to easily implement bucket paging on existing solution. Non of these problems are described in the documentation.