docs: public static NumberVector getPrototype(Model model, Relation<? extends NumberVector> relation) {
      // Mean model contains a numeric Vector
      if(model instanceof MeanModel) {
        return DoubleVector.wrap(((MeanModel) model).getMean());
      }
      // Handle medoid models
      if(model instanceof MedoidModel) {
        return relation.get(((MedoidModel) model).getMedoid());
      }
      if(model instanceof PrototypeModel) {
        Object p = ((PrototypeModel<?>) model).getPrototype();
        if(p instanceof NumberVector) {
          return (NumberVector) p;
        }
        return null; // Inconvertible
      }
      return null;
    }