/**
 * Implements hook_file_validate().
 */
function {{ machine_name }}_file_validate(Drupal\file\FileInterface $file) {
  $errors = [];

  if (!$file->getFilename()) {
    $errors[] = t("The file's name is empty. Please give a name to the file.");
  }
  if (strlen($file->getFilename()) > 255) {
    $errors[] = t("The file's name exceeds the 255 characters limit. Please rename the file and try again.");
  }

  return $errors;
}