code: public static <T,R> void register(Class<T> from, Class<R> to, Function<T,R> transform) {
          REGISTRY.register(from, to, transform);
      }
docs: register a transform function for from type -* to type
  
  @param from class of from type
  @param to   class of to type
  @param transform transform function
  @param <T>  from type
  @param <R>  to type