/**
 * Helper function to determine if input is unset.
 *
 * @param x - the input being tested
 * @returns boolean
 *
 * @example
 * isUnset(null);      // Returns: true
 * isUnset(undefined); // Returns: true
 * isUnset('hello');   // Returns: false
 */
export declare const isUnset: (x: any) => boolean;