presto-main/src/main/java/io/prestosql/operator/aggregation/multimapagg/LegacyGroupedMultimapAggregationState.java/LegacyGroupedMultimapAggregationState/isEmpty
class LegacyGroupedMultimapAggregationState:    @Override
    public boolean isEmpty()
    {
        return keyBlockBuilders.get(getGroupId()) == null;
    }