code: @Override
    public byte[] call(final byte[] memento) {
      LOG.log(Level.FINE, "Task started: sleep for: {0} msec.", this.delay);
      final long ts = System.currentTimeMillis();
      for (long period = this.delay; period > 0; period -= System.currentTimeMillis() - ts) {
        try {
          Thread.sleep(period);
        } catch (final InterruptedException ex) {
          LOG.log(Level.FINEST, "Interrupted: {0}", ex);
        }
      }
      LOG.log(Level.FINE, "Task finished after {0} msec.", System.currentTimeMillis() - ts);
      return null;
    }
docs: Sleep for delay milliseconds and return.
  
  @param memento ignored.
  @return null.