Default to uncategorized

I’ve made the following changes to my copy of the plugin, in absence of a filter. All are in media-categories.php

Added to media_categories_meta_box() (line 140):

if (!get_the_category($post->ID))
{
    $selected_cats = array(1);
} else {
    foreach (get_the_category($post->ID) as $category) {
        $selected_cats[] = $category->cat_ID;
   }
}

and added ‘selected_cats’ => $selected_cats to line 176 as follows:

<?php wp_terms_checklist($post->ID, array('taxonomy' => $taxonomy, 'selected_cats' => $selected_cats, 'popular_cats' => $popular_ids, 'walker' => $custom_walker)) ?>

This succesfully checks the checkbox for the Uncategorized category, when no other category is selected. However, so far, this is only a visual effect and not saved to the database.

Instead of my previous code for line 140:

if (!get_the_category($post->ID))
        {
            wp_set_object_terms($post->ID, 1, 'category');
            $selected_cats = array(1);
        } else {
            foreach (get_the_category($post->ID) as $category) {
                $selected_cats[] = $category->cat_ID;
            }
        }

this saves the default category term 1 (Uncategorized) for Uncategorized posts. Do note that this does not support custom taxonomy.