function uc_stock_adjust($sku, $newStock); not returning any value Iam using uc_stock module functions of ubercart module in my function but not getting result as i want. here is my code:

function my_module_node_presave($node) {  
  if ($node-&gt;type == 'add_stock') {
    if (module_exists('uc_stock') &amp;&amp; function_exists('uc_stock_adjust')) {
      $newStock = $node-&gt;field_stock_value['und'][0]['value'];
      drupal_set_message('new stock :' . $newStock);

      $sku = $node-&gt;field_sku['und'][0]['value'];
      drupal_set_message('sku :'. $sku);

      $key = $node-&gt;field_reference['und'][0]['nid'];
      drupal_set_message('key :'. $key);

      $items = field_get_items('node', $node, 'field_sku');
      drupal_set_message("&lt;pre&gt;" . print_r($items, true) . "&lt;/pre&gt;"); 
      $sku = $items[0];
      drupal_set_message("&lt;pre&gt;" . print_r($sku, true) . "&lt;/pre&gt;");     

      $stock_adjust = uc_stock_adjust($sku, $newStock);
      drupal_set_message('stock_adjust :'.$stock_adjust);

      $stock_set = uc_stock_set($sku, $newStock);
      drupal_set_message('stock_set :'.$stock_set);
    }
  }
}


in my code 



$stock_adjust = uc_stock_adjust($sku, $newStock);

$stock_set = uc_stock_set($sku, $newStock);

the above two functions were returning no value. now anyone can tell me whats the problem in my code
Function uc_stock_adjust has no return value.


  Description: This function adjust a particular product SKU by a
  certain value (a positive integer will add to stock, a negative
  integer will remove from stock).
  
  Parameters:
  $sku - The product SKU that will have its stock level adjusted
  $qty - The quantity to add to the stock level 
  
  Return value: No return value.