Accessing Zend url action helper from a custom action helper in default module
===

So I normally have no problem utilizing the "url" action helper from a custom action helper, when accessing a module, using the following:

$urlHelper = Zend_Controller_Action_HelperBroker::getExistingHelper('url');

But the follow error occurs if the default module (the root url, /) is accessed:

Fatal error: Uncaught exception 'Zend_Controller_Action_Exception' with message 'Action helper "Url" has not been registered with the helper broker' in /home/erahhal/Code/ZendFramework-1.11.12/library/Zend/Controller/Plugin/Broker.php on line 336

What is the root of this problem?