ZF-6381: Second param to Zend_Registry::get() for default value
Add an optional second parameter to Zend_Registry::get()
In the case of if (!$instance->offsetExists($index)) instead of always throwing an exception, look to see if the second param is not null and return that value. If it's null, then go ahead and throw the exception.
This greatly improves the usability of this method as I won't have to always put it in a try/catch block when there is an acceptable default.