parse_query on category page

Hi everybody,

I am triggering the parse_query action to change the default query on category page.
The problem is that I would like to make a different post_status for the post and the attachment.

Null for attachment,
Public or private for post.

function ab_add_posts_attachments_to_category_query() {
   global $wp_query;
   if ( is_category() ) {
      $wp_query->query_vars['post_type'] =  array( 'post', 'attachment' );
      $wp_query->query_vars['post_status'] =  array( null );
      return $wp_query;
   }
}
add_action('parse_query', 'ab_add_posts_attachments_to_category_query');

as you see in my code the post_status is NULL for everything!
thanks!