No file found - get the file object in file upload validate function

I had a form without this "name" parametar, and without that parametar there is just no file object in validate function for file upload

   $form['image']['file']= array(
      '#name' => 'files[advert]',   
      '#type' => 'file',
      '#title' => '
'.t('Add New Image').'
',
      '#description' => t('Upload a file, allowed extensions: jpg, jpeg, png, gif'),
    );

and then you can get it in validate function like below with 'advert'

function item_validate($form, &$form_state)
{
  if ($form_state['input']['image']['select_tags'] == 2) {
  $file = file_save_upload('advert', array(
      'file_validate_is_image' => array(), // Validates file is really an image.
      'file_validate_extensions' => array('png gif jpg jpeg'), // Validate extensions.
    ));