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/**
 * Look for placeholder url and replace it with latest post
 *
 * @param $items
 *
 * @return mixed
 */
function latest_conference_item( $items ) {

	// Get the latest conference
	$latestpost = get_posts( array(
		'numberposts' => 1,
		'orderby'     => 'date',
		'order'       => 'DESC',
		'post_status' => 'publish',
		'post_type'   => 'post'
	) );

	foreach ( $items as $item ) {

		if ( empty( $latestpost ) || '#placeholder' != $item->url ) {
			continue;
		}

		// Replace the placeholder with the real URL
		$item->url = get_permalink( $latestpost[0]->ID ) . 'program';
	}

	return $items;
}

if ( ! is_admin() ) {
	add_filter( 'wp_get_nav_menu_items', 'latest_conference_item', 10 );
}