Date histogram response - Elasticsearch 7.10.0

{
    "aggregations":{
        "nested#my_histo_nested":{
            "doc_count":6,
            "date_histogram#my_histo":{
                "buckets":[
                    {
                        "key_as_string":"2018-04-01T03:00:00.000Z",
                        "key":1522551600000,
                        "doc_count":0
                    },
                    {
                        "key_as_string":"2018-04-01T06:00:00.000Z",
                        "key":1522562400000,
                        "doc_count":0
                    },
                    {
                        "key_as_string":"2018-04-02T03:00:00.000Z",
                        "key":1522638000000,
                        "doc_count":1
                    },
                    {
                        "key_as_string":"2018-04-02T06:00:00.000Z",
                        "key":1522648800000,
                        "doc_count":0
                    },
                    {
                        "key_as_string":"2018-04-03T03:00:00.000Z",
                        "key":1522724400000,
                        "doc_count":3
                    },
                    {
                        "key_as_string":"2018-04-03T06:00:00.000Z",
                        "key":1522735200000,
                        "doc_count":0
                    },
                    {
                        "key_as_string":"2018-04-04T03:00:00.000Z",
                        "key":1522810800000,
                        "doc_count":1
                    },
                    {
                        "key_as_string":"2018-04-04T06:00:00.000Z",
                        "key":1522821600000,
                        "doc_count":0
                    },
                    {
                        "key_as_string":"2018-04-05T06:00:00.000Z",
                        "key":1522908000000,
                        "doc_count":0
                    },
                    {
                        "key_as_string":"2018-04-06T06:00:00.000Z",
                        "key":1522994400000,
                        "doc_count":0
                    },
                    {
                        "key_as_string":"2018-04-07T03:00:00.000Z",
                        "key":1523070000000,
                        "doc_count":1
                    },
                    {
                        "key_as_string":"2018-04-07T06:00:00.000Z",
                        "key":1523080800000,
                        "doc_count":0
                    },
                    {
                        "key_as_string":"2018-04-08T06:00:00.000Z",
                        "key":1523167200000,
                        "doc_count":0
                    },
                    {
                        "key_as_string":"2018-04-09T06:00:00.000Z",
                        "key":1523253600000,
                        "doc_count":0
                    }
                ]
            }
        }
    }
}