/**
 * Implements hook_field_prepare_view().
 */
function {{ machine_name }}_field_prepare_view($entity_type, $entities, $field, $instances, $langcode, &$items) {
  // Sample code from image.module: if there are no images specified at all,
  // use the default image.
  foreach ($entities as $id => $entity) {
    if (empty($items[$id]) && $field['settings']['default_image']) {
      if ($file = file_load($field['settings']['default_image'])) {
        $items[$id][0] = (array) $file + array(
          'is_default' => TRUE,
          'alt' => '',
          'title' => '',
        );
      }
    }
  }
}