/**
 * Converts duration in ms to timestamp.
 *
 * @param expiresIn - **value** in **ms** when access token expires
 * @returns Access token expiration **date** in ISO string format.
 *
 * @category Utilities
 *
 * @example
 * ```ts
 * import { createExpirationDate } from '@ackee/petrus';
 *
 * // expiratioDate will be in following format: "2019-02-19T21:02:57.970Z"
 * const expirationDate = createExpirationDate(3600 * 1000);
 *
 * // VALID:
 * createExpirationDate('3600000');
 * createExpirationDate(null);
 * createExpirationDate(undefined);
 *
 * // INVALID:
 * createExpirationDate('foo');
 * createExpirationDate('foo123');
 * ```
 */
export declare function createExpirationDate(expiresIn: string | number | null | undefined): string | null;