code: public TagSetModel getOrCreate(GraphRewrite event, Set<String> tags)
      {
          Map<Set<String>, Vertex> cache = getCache(event);
          Vertex vertex = cache.get(tags);
          if (vertex == null)
          {
              TagSetModel model = create();
              model.setTags(tags);
              cache.put(tags, model.getElement());
              return model;
          }
          else
          {
              return frame(vertex);
          }
      }
docs: This essentially ensures that we only store a single Vertex for each unique "Set" of tags.