If a min aggregation is used inside a terms aggregation, the result doesn't contain any buckets for the terms aggregation, as long as no mapping exists for the min aggregation field (e.g. there is no value for that field and dynamic mapping is used)
Once a mapping for the field exists, the result contains the buckets for the terms aggregation.
The max aggregation works independent of an existing mapping for the field
Use the following shell script to reproduce the issue:
# min aggregation with issue
curl -XDELETE "http://localhost:9200/test"
curl -XPUT "http://localhost:9200/test/_doc/1" -H 'Content-Type: application/json' -d'{ "name": "A", "number": null}'
# min aggregation with empty result for the terms aggregation
sleep 2
echo 'MIN AGGREGATION WITH EMPTY RESULT'
curl -XGET "http://localhost:9200/test/_search" -H 'Content-Type: application/json' -d'{ "size": 0, "aggs": { "terms": { "terms": { "field": "name.keyword" }, "aggs": { "agg": { "min": { "field": "number" } } } } }}'
# specify mapping for the number field
curl -XPOST "http://localhost:9200/test/_mapping" -H 'Content-Type: application/json' -d'{ "properties": { "number": { "type": "long" } }}'
sleep 2
# now the result contains buckets for the terms aggregation
echo 'MIN AGGREGATION WITH RESULT'
curl -XGET "http://localhost:9200/test/_search" -H 'Content-Type: application/json' -d'{ "size": 0, "aggs": { "terms": { "terms": { "field": "name.keyword" }, "aggs": { "agg": { "min": { "field": "number" } } } } }}'
# max aggregation works independet of an existing mapping
curl -XDELETE "http://localhost:9200/test"
curl -XPUT "http://localhost:9200/test/_doc/1" -H 'Content-Type: application/json' -d'{ "name": "A", "number": null}'
sleep 2
echo 'MAX AGGREGATION WITH RESULT'
curl -XGET "http://localhost:9200/test/_search" -H 'Content-Type: application/json' -d'{ "size": 0, "aggs": { "terms": { "terms": { "field": "name.keyword" }, "aggs": { "agg": { "max": { "field": "number" } } } } }}'