docs: @Override
      public Map<String, PMML4Model> getRootModels() {
          Map<String, PMML4Model> rootModels = new HashMap<>();
          for (PMML4Model model : this.modelsMap.values()) {
              if (model.getParentModel() == null) {
                  rootModels.put(model.getModelId(), model);
              }
          }
          return rootModels;
      }