code: public void setFooter(String key, String value)
    {
      Objects.requireNonNull(value);
  
      int i = 0;
      boolean hasFooter = false;
  
      for (i = _footerKeys.size() - 1; i >= 0; i--) {
        String oldKey = _footerKeys.get(i);
  
        if (oldKey.equalsIgnoreCase(key)) {
          if (hasFooter) {
            _footerKeys.remove(i);
            _footerValues.remove(i);
          }
          else {
            hasFooter = true;
  
            _footerValues.set(i, value);
          }
        }
      }
  
      if (! hasFooter) {
        _footerKeys.add(key);
        _footerValues.add(value);
      }
    }
docs: Sets a footer, replacing an already-existing footer
  
  @param key the header key to set.
  @param value the header value to set.