code: @SuppressWarnings("PMD.AvoidInstantiatingObjectsInLoops")
      private static Iterable<String> extend(final Response res,
          final Iterable<? extends CharSequence> headers) throws IOException {
          Response resp = res;
          for (final CharSequence hdr: headers) {
              resp = new RsWithHeader(resp, hdr);
          }
          return resp.head();
      }
docs: Add to head additional headers.
  @param res Original response
  @param headers Values witch will be added to head
  @return Head with additional headers
  @throws IOException If fails