java.lang.ClassNotFoundException: org.elasticsearch.search.aggregations.metrics.cardinality.ParsedCardinality

Elastic Stack Elasticsearch
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@javanna @rjernst @dadoonet

I think I have figured out the NoClassDefFoundError problem.

In ES 7.x Lib, there is:
     import org.elasticsearch.search.aggregations.metrics.CardinalityAggregationBuilder;
     import org.elasticsearch.search.aggregations.metrics.ParsedCardinality;

In ES 6.x lib, it is:
     import org.elasticsearch.search.aggregations.metrics.cardinality.CardinalityAggregationBuilder;
     import org.elasticsearch.search.aggregations.metrics.cardinality.ParsedCardinality;

So, when using 6.x HLRC, it is expecting   
    org.elasticsearch.search.aggregations.metrics.cardinality.ParsedCardinality.
But I am using ES 7.x lib which does not have this class, but the
    org.elasticsearch.search.aggregations.metrics.ParsedCardinality

Is there any reason for the name change from 6.x to 7.x? I did not see it in the breaking changes note.
I have no easy way of getting around this problem. Lower ES lib to 6.x will have totalHit() as 0 when accessing ES 7.x, since 7.x change the totalHit() to an object with value and relation, 6.x just a long value.
Anyway Elastic.co can change HLRC 6.x lib or 7.x ES lib to make HLRC 6.x compatible with 7.x ES?
Thanks