Add background-image or background-color to nav menu item using ACF

image_bg_color_nav_menu_item_ACF.php

<?php
//add background-image or background-color to nav menu item using ACF
add_filter('wp_nav_menu_items', 'new_nav_menu_items', 10, 2);
function new_nav_menu_items($items, $args) {

    preg_match_all('/menu-item-([0-9]{1,10})"/ ', $items, $matches);

    if (isset($matches[0]) && isset($matches[1])) {
        foreach ($matches[0] as $k => $repl) {
            $post_id = $matches[1][$k];
            if ($image_id = get_field('image_menu', $post_id))
                $st = "style='". image_src($image_id, 'free', 1) ."' ";
            elseif($bg = get_field('background_color_menu', $post_id))
                $st = "style='background-color: $bg' ";
            else
                $st = "";

            $items = str_replace($repl, "$repl $st ", $items);
        }
    }

    return $items;
}