Hi,
I think it's a bug that CompositeAggregation histograms does not have a way to "fill empty interval buckets". It is the default behaviour in normal Histogram Aggregations.
The documentation says in: Histogram Aggregation | Elasticsearch Guide [6.7] | Elastic
By default the response will fill gaps in the histogram with empty buckets.
This is more important with DateHistograms because supporting Elasticsearch time interval calculation at client side is not so trivial.
Tried to create github issue but it was closed as "question". So here I am.
-Tuomas