Major Description
Following up on SOLR-7804 lead to this error which i'm splitting off into it's own issue. the nuthsell is that if you combine facet.missing, facet.pivot.mincount, and facet.sort=index you might get incorrect counts (or no counts at all) for the missing value of a pivot.
fairly easy to reproduce the most extreme aspect of the problem (not getting a missing count back even though it's above the minumum)...
bin/solr -e cloud -noprompt
bin/post -c gettingstarted example/exampledocs/*.xml
http://localhost:8983/solr/gettingstarted/query?rows=0&q=*:*&facet=true&facet.pivot=inStock&facet.missing=true
...
"facet_pivot":{
"inStock":[{
"field":"inStock",
"value":true,
"count":17},
{
"field":"inStock",
"value":false,
"count":4},
{
"field":"inStock",
"value":null,
"count":11}]}}}
http://localhost:8983/solr/gettingstarted/query?rows=0&q=*:*&facet=true&facet.pivot=inStock&facet.missing=true&facet.pivot.mincount=10
...
"facet_pivot":{
"inStock":[{
"field":"inStock",
"value":true,
"count":17},
{
"field":"inStock",
"value":null,
"count":11}]}}}
http://localhost:8983/solr/gettingstarted/query?rows=0&q=*:*&facet=true&facet.pivot=inStock&facet.missing=true&facet.pivot.mincount=10&facet.sort=index
...
"facet_pivot":{
"inStock":[{
"field":"inStock",
"value":true,
"count":17}]}}}
...note that in the last example, the 'null' count is gone (even though it's above the minimum) just because we changed the facet.sort.