if( ! function_exists( 'safir_add_the_logo_onto_the_menu' ) ){
    /**
     * @param unknown_type $items
     * @param unknown_type $args
     */
    function safir_add_the_logo_onto_the_menu( $items, $args ) {
        // Change the custom logo url here or leave for default logo that is uploaded on WP Customiser.
        $the_custom_logo_url    =   get_header_image();

        $output =   '';

        if( $args->theme_location == 'primary' && !empty( $the_custom_logo_url ) ){
            $output .= '<li class="menu-logo" style="display:none">';
                $output .= '
                    <a href="'. esc_url( home_url() ) .'">
                        <img alt="'. esc_attr( get_bloginfo( 'description' ) ) .'" src="'. esc_url( $the_custom_logo_url ) .'">
                    </a>
                ';
            $output .= '</li>';
        }
        if( ! empty( $output ) ){
            return $output . $items;
        }
        return $items;
    }
    add_filter('wp_nav_menu_items', 'safir_add_the_logo_onto_the_menu', 10, 2);
}