Small Bug in Joomla System Message Rendering

I have found a bug in Joomla. Don't know where to put it. thats why putting here.
If anybody know please pick it up and gives to joomla developers.

This bug is related to rendering joomla system messages.
The messages were empty, still the system was showing that.

I modified file --> libraries\joomla\document\html\renderer\message.php (joomla 1.5.8)
by adding line in RED.

It fixed my issue.

// Build the sorted message list
if (is_array($messages) && count($messages)) {
foreach ($messages as $msg)
{
if (isset($msg['type']) && isset($msg['message'])) {
if(!empty($msg['message']))
$lists[$msg['type']][] = $msg['message'];
}
}
}