code: public void addRelationshipFilter(RelatedFinder relatedFinder, Operation filter)
      {
          Operation existing = this.filters.get(relatedFinder);
          this.filters.put(relatedFinder, existing == null ? filter : existing.or(filter));
      }
docs: Add a filter to be applied to the result of a traversed relationship.
  
  @param relatedFinder - the relationship to apply the filter to
  @param filter - the filter to apply