PHP Logic

Hi, I have a fairly straight forward piece of PHP code:

<?php

$menu_to_count =  wp_nav_menu( array(
  'theme_location' => 'primary',
  'sub_menu' => true,
  'echo' => false
) );

$menu_items = substr_count( $menu_to_count, 'class="menu-item ' ); 

if ( $menu_items != 0 ) { wp_nav_menu( array('theme_location' => 'primary','sub_menu' => true,'direct_parent' => true) );
									} else {
										echo "none"; } ?>

The problem is the line wp_nav_menu( array(‘theme_location’ => ‘primary’,’sub_menu’ => true,’direct_parent’ => true) ) for when it evaluates to true. If I change that to a simple echo (“yes”) then it is fine – which means I must be missing some logic. Any thoughts?