code: @Override
      public Promise<Void> link(String link, String existing) {
          return adapter.toPromise(handler -> vertx.fileSystem().link(link, existing, handler));
      }
docs: Create a hard link on the file system from {@code link} to {@code existing}, asynchronously.
  
  @param link     the link
  @param existing the link destination
  @return a promise for completion