--- /dev/null
+// Copyright (C) The Arvados Authors. All rights reserved.
+//
+// SPDX-License-Identifier: AGPL-3.0
+
+export const optional = (validator: (value: any) => string | undefined) =>
+ (value: any) =>
+ value === undefined || value === null || value === '' ? undefined : validator(value);
\ No newline at end of file