code: public RequestHandler<I, O> end(RequestHandler<II, OO> handler) {
          return interceptor.intercept(handler);
      }
docs: Terminates this chain with the passed {@link RequestHandler} and returns a {@link RequestHandler} to be
  used by a {@link HttpServer}
  
  @param handler Request handler to use.
  
  @return A request handler that wires the interceptor chain, to be used with {@link HttpServer} instead of
  directly using the passed {@code handler}