Could someone explain the reasoning behind having to specify "_agg" : {} if script parameters are specified in the scripted metric aggregation (from this page: https://www.elastic.co/guide/en/elasticsearch/reference/5.5/search-aggregations-metrics-scripted-metric-aggregation.html).
It seems like the _agg variable should always start out as empty, so it would make sense to include it by default even if other parameters are specified. In the native Java API, I see in ScriptedMetricAggregatorFactory that the _agg variable is passed in if no params are specified, so I was thinking it should just be passed in either way.
Maybe there's something I'm missing here, so thanks in advance for answering!