Field collection fix for host migration

/**
 * Implements Migration::prepare().
 * This func fix empty fc's on migrate update operation.
 * Used as fix while performs updates,
 * drush mi AlNodeInstitution --idlist="8013" --force --update.
 */
public function prepare($entity, stdClass $row) {
  // Don't run on initial import only on update.
  if (isset($entity->nid)) {
    // Load the original node object.
    $original = node_load($entity->nid);
    self::removeEmptyFcItems($entity, $original, array('field_fc_al_image'));
  }
}

/**
 * Clear & set field collection items.
 *
 * Clear from empty first fc item on entity,
 * and resolve existing field collections from original entity object.
 *
 * @param mixed $entity
 *   Object from migrate that will be updated later.
 * @param mixed $original
 *   Original entity object loaded via entity_load().
 * @param array $fc
 *   An array of field collection names that should be fixed.
 */
protected function removeEmptyFcItems($entity, $original, $fc) {
  foreach ($fc as $fc_name) {
    if (!empty($original->{$fc_name}[LANGUAGE_NONE])
      && count($original->{$fc_name}[LANGUAGE_NONE]) > 1
    ) {
      $original_wrapper = entity_metadata_wrapper(
        _al_migrate_entity_type_get_name($original),
        $original
      );

      if (!empty($original_wrapper->{$fc_name}[0])) {
        foreach ($original_wrapper->{$fc_name} as $idx => $fc_item) {
          if (!empty($fc_item)
            && method_exists($fc_item, 'value')
          ) {
            if ($fc_item->value() === NULL) {
              unset($original->{$fc_name}[LANGUAGE_NONE][$idx]);
            }
          }
        }
      }
    }
    // Add original field collection data to our current object.
    $entity->$fc_name = $original->$fc_name;
  }
}