code: public RuntimeTypeAdapterFactory<T> registerSubtype(Class<? extends T> type) {
      return registerSubtype(type, type.getSimpleName());
    }
docs: Registers {@code type} identified by its {@link Class#getSimpleName simple
  name}. Labels are case sensitive.
  
  @throws IllegalArgumentException if either {@code type} or its simple name
  have already been registered on this type adapter.