code: public Registration register (Registration registration) {
  		int id = registration.getId();
  		if (id < 0) throw new IllegalArgumentException("id must be > 0: " + id);
  
  		Registration existing = classResolver.unregister(id);
  		if (DEBUG && existing != null && existing.getType() != registration.getType())
  			debug("kryo", "Registration overwritten: " + existing + " -> " + registration);
  
  		return classResolver.register(registration);
  	}
docs: Stores the specified registration. If the ID is already in use by the same type, the old entry is overwritten. Registering
  a primitive also affects the corresponding primitive wrapper.
  <p>
  IDs must be the same at deserialization as they were for serialization.
  <p>
  Registration can be suclassed to efficiently store per type information, accessible in serializers via
  {@link Kryo#getRegistration(Class)}.