I've added support in the missing setting in bucket aggregations (terms and date histogram) :
Example for graph w/ the new setting :
ElasticSearch Terms & Date Histogram: Support 'missing' setting
feat(elasticsearch): Added support for Missing option (bucket) for te…
…rms aggregation, refactoring PR #4244, thx @shanielh
merged to master, sorry for taking the time to merge this.
Also removed the date histogram missing option. not sure if that was supposed to work, did not make sense as the bucket for missing timestamp field does not return a valid date.