def get_gradebook_column_notification_session(self, gradebook_column_receiver=None, proxy=None):
if proxy is None:<EOL><INDENT>raise NullArgument()<EOL><DEDENT>raise Unimplemented()<EOL>
Gets the notification session for notifications pertaining to gradebook column changes.

        arg:    gradebook_column_receiver
                (osid.grading.GradebookColumnReceiver): the grade system
                receiver
        arg:    proxy (osid.proxy.Proxy): a proxy
        return: (osid.grading.GradebookColumnNotificationSession) - a
                ``GradebookColumnNotificationSession``
        raise:  NullArgument - ``gradebook_column_receiver`` or
                ``proxy`` is ``null``
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented -
                ``supports_gradebook_column_notification()`` is
                ``false``
        *compliance: optional -- This method must be implemented if
        ``supports_gradebook_column_notification()`` is ``true``.*