Worepress - No listar en los posts los posts que no tengan una categoria definida.

WP-no-category.php

//if the post is category "uncategorized" or child of "uncategorized" as the main category, change the permalink rule of "/%category%/%postname%" to "/%postname%"
function my_pre_post_link($permalink, $post, $leavename)
{
    if ($post->post_type != 'post') {
        return $permalink;
    }
    $cats = get_the_category($post->ID);
    if (!count($cats)) {
        return $permalink;
    }

    usort($cats, '_usort_terms_by_ID');
    $category_object = apply_filters('post_link_category', $cats[0], $cats, $post);

    $category_object = get_term($category_object, 'category');

    return _clear_uncategorized($category_object, $permalink);
}

function _clear_uncategorized($cat, $permalink)
{
    if ($cat->slug == 'sin-categoria') {
        return str_replace('%category%/', '', $permalink);
    }
    $parent = $cat->parent;
    if (!$parent) {
        return $permalink;
    }

    return _clear_uncategorized($parent, $permalink);
}