Gets an asset search session for the given repository.

        arg:    repository_id (osid.id.Id): the Id of the repository
        return: (osid.repository.AssetSearchSession) - an
                AssetSearchSession
        raise:  NotFound - repository_id not found
        raise:  NullArgument - repository_id is null
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - supports_asset_search() or
                supports_visible_federation() is false
        compliance: optional - This method must be implemented if
                    supports_asset_search() and
                    supports_visible_federation() are true.

def get_asset_search_session_for_repository(self, repository_id=None):
        """Gets an asset search session for the given repository.

        arg:    repository_id (osid.id.Id): the Id of the repository
        return: (osid.repository.AssetSearchSession) - an
                AssetSearchSession
        raise:  NotFound - repository_id not found
        raise:  NullArgument - repository_id is null
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - supports_asset_search() or
                supports_visible_federation() is false
        compliance: optional - This method must be implemented if
                    supports_asset_search() and
                    supports_visible_federation() are true.

        """
        if not repository_id:
            raise NullArgument()
        if not self.supports_asset_search():
            raise Unimplemented()
        try:
            from . import sessions
        except ImportError:
            raise OperationFailed('import error')
        try:
            session = sessions.AssetSearchSession(repository_id,
                                                  proxy=self._proxy,
                                                  runtime=self._runtime)
        except AttributeError:
            raise OperationFailed('attribute error')
        return session