code: @Override public GBMModel createImpl() {
      GBMV3.GBMParametersV3 p = this.parameters;
      GBMModel.GBMParameters parms = p.createImpl();
      return new GBMModel(model_id.key(), parms, new GBMModel.GBMOutput(null));
    }
docs: Version&Schema-specific filling into the impl