code: @Override
    public Long renamenx(final byte[] oldkey, final byte[] newkey) {
      checkIsInMultiOrPipeline();
      client.renamenx(oldkey, newkey);
      return client.getIntegerReply();
    }
docs: Rename oldkey into newkey but fails if the destination key newkey already exists.
  <p>
  Time complexity: O(1)
  @param oldkey
  @param newkey
  @return Integer reply, specifically: 1 if the key was renamed 0 if the target key already exist