code: public IndexingConfigurationBuilder addKeyTransformer(Class<?> keyClass, Class<?> keyTransformerClass) {
        Map<Class<?>, Class<?>> indexedEntities = keyTransformers();
        indexedEntities.put(keyClass, keyTransformerClass);
        attributes.attribute(KEY_TRANSFORMERS).set(indexedEntities);
        return this;
     }
docs: Registers a transformer for a key class.
  
  @param keyClass the class of the key
  @param keyTransformerClass the class of the org.infinispan.query.Transformer that handles this key type
  @return <code>this</code>, for method chaining