Difference of min and max aggregation for missing values

Elastic Stack Elasticsearch
1

Hi,
I'm trying to understand the difference of the min and max aggregation for documents where all field values are missing.

Let's imagine the following simple document:

PUT /test/_doc/1
{
  "name": "A",
  "number": null
}

If I want to get only the max or min value for the number field, the query in both cases results in the same -> null

GET /test/_search
{
  "size": 0, 
  "aggs": {
    "agg": {
      "min": {
        "field": "number"
      }
    }
  }
}

{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "agg" : {
      "value" : null
    }
  }
}

However, if I use the min or max agg inside a terms aggregation, the result is different for min and max.

GET /test/_search
{
  "size": 0, 
  "aggs": {
    "terms": {
      "terms": {
        "field": "name.keyword"
      },
      "aggs": {
        "agg": {
          "max": {
            "field": "number"
          }
        }
      }
    }
  }
}

For max agg, the result looks similar. It contains a bucket for name value 'A' and null as the value for the max agg:

{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "terms" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 0,
      "buckets" : [
        {
          "key" : "A",
          "doc_count" : 1,
          "agg" : {
            "value" : null
          }
        }
      ]
    }
  }
}

Whereas for the min aggregation the bucket with the name value 'A' is missing in the result completely:

GET /test/_search
{
  "size": 0, 
  "aggs": {
    "terms": {
      "terms": {
        "field": "name.keyword"
      },
      "aggs": {
        "agg": {
          "min": {
            "field": "number"
          }
        }
      }
    }
  }
}

{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  },
  "aggregations" : {
    "terms" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 0,
      "buckets" : [ ]
    }
  }
}

Is there anyone who could give some details about that behavior?

Many thanks!!

2

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