code: public void writeAttribute(String name, Object ... values)
    {
      if (!_isElementOpen)
        throw new IllegalStateException("no open element");
  
      _isElementOpen = false;
  
      try {
        _strategy.writeAttribute(this, name, values);
      }
      finally {
        _isElementOpen = true;
      }
  
    }
docs: Write an attribute with multiple values, separated by space, if a value
  is null nothing is written.
  
  @throws IllegalStateException if the is no element is open