I think it is not OK because of the lack of symetry of the equals method: although `new ClosestNestedParentFilter(parentAggregator).equals(parentFilter)` would return true, `parentFilter.equals(new ClosestNestedParentFilter(parentAggregator))` would return false, which means we might pollute the filter cache with a new filter that will never be reused every time this aggregation is used. So I think we need to fix the root issue, that is that parent aggregators should be fully constructed before constructing sub aggregators, before fixing this one.