code: public void addDefaultSerializer (Class type, Serializer serializer) {
  		if (type == null) throw new IllegalArgumentException("type cannot be null.");
  		if (serializer == null) throw new IllegalArgumentException("serializer cannot be null.");
  		insertDefaultSerializer(type, new SingletonSerializerFactory(serializer));
  	}
docs: Instances of the specified class will use the specified serializer when {@link #register(Class)} or
  {@link #register(Class, int)} are called.
  @see #setDefaultSerializer(Class)