anchor.diff:  
       final fields = {
         'key': key,
  -      'acl': predefinedAcl,
         'Expires': expirationString,
         'GoogleAccessId': result.googleAccessId,
         'policy': policyString,
  
positive.code:     String object,
      Duration lifetime, {
      String? successRedirectUrl,
      String predefinedAcl = 'project-private',
      int maxUploadSize = maxUploadSize,
    }) async {
      final now = clock.now().toUtc();
  
negative.code:     final key = '$bucket/$object';
      final conditions = [
        {'key': key},
        {'expires': expirationString},
        if (successRedirectUrl != null)
          {'success_action_redirect': successRedirectUrl},
  