docs: protected void removePreviousRelation(Relation<?> relation) {
      if(keep) {
        return;
      }
      boolean first = true;
      for(It<Index> it = relation.getHierarchy().iterDescendants(relation).filter(Index.class); it.valid(); it.advance()) {
        if(first) {
          Logging.getLogger(getClass()).statistics("Index statistics when removing initial data relation.");
          first = false;
        }
        it.get().logStatistics();
      }
      ResultUtil.removeRecursive(relation.getHierarchy(), relation);
    }