Nav walker

  <?php  /* In HEADER file PLUS 'wp_bootstrap_navwalker.php' has been uploaded to root of custom theme */
            wp_nav_menu( array(
                'menu'              => 'primary',
                'theme_location'    => 'primary',
                'depth'             => 2,
                'container'         => 'div',
                'container_class'   => 'collapse navbar-collapse',
        'container_id'      => 'bs-example-navbar-collapse-1',
                'menu_class'        => 'nav navbar-nav',
                'fallback_cb'       => 'wp_bootstrap_navwalker::fallback',
                'walker'            => new wp_bootstrap_navwalker())

/* in FUNCTIONS file */
function register_my_menus() {
  register_nav_menus(
    array(

      'primary' => _('Primary Menu', 'jrmasonry')
  );
}
add_action( 'init', 'register_my_menus' );

?>