def get_qualifier_hierarchy_session(self, qualifier_hierarchy_id=None):
raise Unimplemented()<EOL>
Gets the ``OsidSession`` associated with the qualifier hierarchy traversal service.

        The authorization service uses distinct hierarchies that can be
        managed through a Hierarchy OSID.

        arg:    qualifier_hierarchy_id (osid.id.Id): the ``Id`` of a
                qualifier hierarchy
        return: (osid.authorization.QualifierHierarchySession) - a
                ``QualifierHierarchySession``
        raise:  NotFound - ``qualifier_hierarchy_id`` not found
        raise:  NullArgument - ``qualifier_hierarchy_id`` is ``null``
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - ``supports_qualifier_hierarchy()`` is
                ``false``
        *compliance: optional -- This method must be implemented if
        ``supports_qualifier_hierarchy()`` is ``true``.*