function UnsubscriptionError(errors) {
        _super.call(this);
        this.errors = errors;
        var err = Error.call(this, errors ?
            errors.length + " errors occurred during unsubscription:\n  " + errors.map(function (err, i) { return ((i + 1) + ") " + err.toString()); }).join('\n  ') : '');
        this.name = err.name = 'UnsubscriptionError';
        this.stack = err.stack;
        this.message = err.message;
    }
An error thrown when one or more errors have occurred during the
`unsubscribe` of a {@link Subscription}.