def get_hierarchy_structure_notification_session(self, hierarchy_structure_receiver=None, proxy=None):
if proxy is None:<EOL><INDENT>raise NullArgument()<EOL><DEDENT>raise Unimplemented()<EOL>
Gets the session for subscribing to notifications of changes within a hierarchy structure.

        arg:    hierarchy_structure_receiver
                (osid.hierarchy.HierarchyStructureReceiver): a receiver
        arg:    proxy (osid.proxy.Proxy): a proxy
        return: (osid.hierarchy.HierarchyStructureNotificationSession) -
                a ``HierarchyStructureNotificationSession``
        raise:  NullArgument - ``hierarchy_structure_receiver`` or
                ``proxy`` is ``null``
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented -
                ``supports_hierarchy_structure_notification()`` is
                ``false``
        *compliance: optional -- This method must be implemented if
        ``supports_hierarchy_structure_notification()`` is ``true``.*