code: public Registration register (Class type) {
  		Registration registration = classResolver.getRegistration(type);
  		if (registration != null) return registration;
  		return register(type, getDefaultSerializer(type));
  	}
docs: Registers the class using the lowest, next available integer ID and the {@link Kryo#getDefaultSerializer(Class) default
  serializer}. If the class is already registered, no change will be made and the existing registration will be returned.
  Registering a primitive also affects the corresponding primitive wrapper.
  <p>
  Because the ID assigned is affected by the IDs registered before it, the order classes are registered is important when
  using this method. The order must be the same at deserialization as it was for serialization.