Invalid argument supplied for foreach() in /public_html/modules/category/category.module on line 1306 , please help

Hi,
I may have solved it myzelf.
I think a module excedentally used $node without it being an array, so I check this again on the function aroudnd linke 1306.
The code was:

/**
 * Implementation of hook_nodeapi('update_index').
 */
function category_node_update_index(&$node) {
  $output = array();
  foreach ($node->category as $cat) {
    $output[] = $cat->title;
  }
  if (count($output)) {
    return '<strong>('. implode(', ', $output) .')</strong>';
  }
}

The new code I check if $node->category is an array.


/**
* Implementation of hook_nodeapi('update_index').
*/
function category_node_update_index(&$node) {
$output = array();
if (is_array($node->category)) {
foreach ($node->category as $cat) {
$output[] = $cat->title;
}
if (count($output)) {
return '('. implode(', ', $output) .')';
}
}
}


SO I added if (is_array($node->category)) { to the code.
Is this correct?
Please help.
greetings,
Martijn