The second parameter for module_load_include() is not necessary when it is equal to the first parameter

The module calls module_load_include() as module_load_include('inc', 'drupal_queue', 'drupal_queue'); it could call the function as module_load_include('inc', 'drupal_queue') because when the second parameter is not given, the function will set it to the same value of the first parameter.

function module_load_include($type, $module, $name = NULL) {
  if (empty($name)) {
    $name = $module;
  }
  // …
}