Strict warning: Only variables should be passed by reference in search404_page()

Hi there, thanks for the module first off. I think this is a great idea. I am currently running into an issue on the search results page.

Anytime the search 404 module is invoked (when a page that doesnt exist is viewed) I receive the following warning at the top of the page:

"Strict warning: Only variables should be passed by reference in search404_page() (line 181 of home/cps/www/sites/all/modules/search404/search404.module)."

The search works fine though as the expected results are returned and the search form is correctly rendered:

The line in question is:
$output = drupal_render(drupal_get_form('search_form', NULL, empty($keys) ? '' : $keys, 'node')) . drupal_render($results);

My first thought was to put the drupal_render($results) on its own line and concatenate it to the $output variable:

        $output = drupal_render(drupal_get_form('search_form', NULL, empty($keys) ? '' : $keys, 'node')));
	$output.= drupal_render($results);

This simply confirmed that the issue lies in the rendering of the search form and not the rendering of the results.

This actually breaks down I believe, to the form_state argument required by the search_form function (http://api.drupal.org/api/drupal/modules--search--search.module/function...). Currently the call is simply passing null, which is why the Strict Warning is occurring.

Not really sure what we should pass instead, this form doesnt really need a state as far as I can tell.