Issue #3171579 by ankithashetty, matthiasm11: Custom fields empty check

  if ($files_uploaded) {

    // Get replace option.

    $fileUploadService = \Drupal::service('file_upload_options.file_upload_service');

    /** @var \Drupal\Core\Config\ImmutableConfig $config */

    $config = $fileUploadService->getConfig();

    $replaceOption = FileSystemInterface::EXISTS_RENAME;

    if ($isCustomField) {

      $replaceOption = $fileUploadService->getConfig()->get('custom_fields')[$fileId];

      $customFields = $config->get('custom_fields');

      if (!empty($customFields[$fileId])) {

        $replaceOption = $customFields[$fileId];

      }

    }

    else {

      $replaceOption = $fileUploadService->getConfig()->get('upload_option.' . $fileId);

      $replaceOption = $config->get('upload_option.' . $fileId);

    }

    if (!$files = _file_save_upload_from_form($element, $form_state, NULL, $replaceOption)) {