protected function get_taxonomies() {
        $taxonomies = explode(',', $this->raw_get('taxonomies'));

        // Indexing first level at 1.
        array_unshift($taxonomies, null);
        unset($taxonomies[0]);

        // Ensure that we do not return empty levels.
        foreach ($taxonomies as $i => $taxonomy) {
            if (empty($taxonomy)) {
                $taxonomies[$i] = self::TAXONOMY_COMPETENCY;
            }
        }

        return $taxonomies;
    }