Scriptet metric aggregation as sub aggregation after date histogram

Elastic Stack Elasticsearch
1

Hi,
I'm trying to use a scripted metric aggregation as sub aggregation after a date histogram aggregation and I'm getting some errors: 'Cannot invoke method getAt() on null object'

If I do this same scripted metric aggregation after another type of bucket aggregation (non date histogram) then everything works.

Does anybody know why this type of query is failing after a date histogram aggregation?

script:
{
_ "query":{_
_ "bool": {_
_ "must": [_
_ {"bool": {_
_ "should": [_
_ {"term": {"host": "pvx9alfcl1"}},_
_ {"term": {"host": "pvx9alfcl2"}}_
_ ]_
_ }},_
_ {"term": {"HTTP_url": "download"}}_
_ ]_
_ }_
_ },_
_ "aggs": {_
_ "requests_over_time" : {_
_ "date_histogram" : {_
_ "field": "@timestamp",_
_ "interval" : "1d"_
_ },_
_ "aggs": {_
_ "profit": {_
_ "scripted_metric": {_
_ "init_script" : {_
_ "file": "script_init_01",
_ "lang": "groovy"_
_ },_
_ "map_script" : {_
_ "file": "script_map_01",
_ "lang": "groovy"_
_ },_
_ "combine_script" : {_
_ "file": "script_combine_01",
_ "lang": "groovy"_
_ },_
_ "reduce_script" : {_
_ "file": "script_reduce_01",
_ "lang": "groovy"_
_ }_
_ }_
_ }_
_ }_
_ }_
_ }_
}

regards,
Michel