Prototype Ajax.PeriodicalUpdater inserts empty string when server unreachable

var updater = new Ajax.PeriodicalUpdater('content', '/Doc?'+d.getTime(),
  {
    method: 'post',
    frequency: 5,
  });

new Ajax.PeriodicalUpdater({success: 'content'}, '/Doc?'+d.getTime(),
  {
    method: 'post',
    frequency: 5,
  });

function requestMoreInfo(){
new Ajax.Request('url',
  {
    method:'get',
    parameters:  "someget=here",
    onSuccess: handleTheReturn
  });

}

function handleTheReturn(reply){
    var newMessages = eval('(' + reply.responseText + ')');
    //update your element or whatever
}

new PeriodicalExecuter(requestMoreInfo, 20);

<html>
<head>
<title></title>
<script type="text/javascript" src="/Prototype"></script>
<script type="text/javascript">
var css;
var css_data;

function load_content()
{
  var d = new Date();

  css = document.createElement('style');
  css.setAttribute('type', 'text/css');
  if(css.styleSheet) { css.styleSheet.cssText = '';} //Because IE is evil
  else { css_data = document.createTextNode(''); css.appendChild(css_data); } //And everyone else is cool
  document.getElementsByTagName("head")[0].appendChild(css);

  var updater = new Ajax.PeriodicalUpdater({success: 'content'}, '/%doc_path%?'+d.getTime(),
  {
    method: 'post',
    frequency: 5,
    onSuccess: function(transport) {
          new Ajax.Request('/%css_path%?'+d.getTime(), {
              method: 'post',
              onSuccess: function(transport) {
                if(css.styleSheet) { css.styleSheet.cssText = transport.responseText}
                else {
                    var new_css_data = document.createTextNode(transport.responseText);
                    css.replaceChild(new_css_data, css_data);
                    css_data = new_css_data;
                }
              }
          });
          new Ajax.Request('/%title_path%?'+d.getTime(), {
              method: 'post',
              onSuccess: function(transport) {
                document.title = transport.responseText;
              }
          });
    }
  });
}

</script>

</head>

<body>
<div id="content"></div>

<script type="text/javascript">
    load_content();
</script>

</body>
</html>

new Ajax.PeriodicalUpdater('content', 'url', {
    frequency: 5,
    on0: function(requester, exception) {
        alert("ERROR 0");
    }
});