使用Zend Framework检测Amazon RequestThrottled错误

I am using the Amazon Advertising API based on the Zend Framework 2 Amazon Zend_Service. Is there any way to detect when a RequestThrottled error occurs? An example of such an error can be seen here.

Unfortunately the totalResult method also returns 0 on a ResultSet when such an error occurred. So it does not seem to be possible to differentiate an empty response from an error message response. Any ideas on how to deal with that?

For now I solved it by adding a new method to the ResultSet class:

public function hasError()
{
    return ($this->_xpath->evaluate('name(/*)') == 'ItemSearchErrorResponse');
}