function isUndefined(value) {
      return value === undefined;
    }
Checks if `value` is `undefined`.

@static
@since 0.1.0
@memberOf _
@category Lang
@param {*} value The value to check.
@returns {boolean} Returns `true` if `value` is `undefined`, else `false`.
@example

_.isUndefined(void 0);
// => true

_.isUndefined(null);
// => false