Views in panels breaks RSS feed

I have confirmed that the same problem exists when a view is presented through a viewfield. The RSS link points to the URL of the view rather than the URL of the view plus /feed.

Well I tracked down the source of the problem, I believe.

In view_node.inc, there's this function:

function views_post_view_make_args($view, $feed_id, $arg) {
  // assemble the URL
  $args = array();
  foreach ($view->argument as $id => $argdata) {
    if (isset($view->args[$id])) {
      $args[] = $view->args[$id];
    } else {
      if ($argdata['id'] == $feed_id) {
        $args[] = $arg;
      }
      else if ($argdata['argdefault'] != 1) {
        $args[] = '*';
      }
    }
  }
  
  return $args;
}

Note the isset() check. The problem is that if you are using a view through a viewfield or panel, the argument field will (sometimes?) be set to empty string if you're not specifying anything. Empty string is not null, therefore the isset() returns true, and the code dutifully returns "" as the argument to append.

By changing the isset check to if (!empty($view->args[$id])) {, it gracefully handles both NULL and empty string, thus giving the correct default.

Patch attached against 5.x-dev.