code: def get_composition_admin_session_for_repository(self, repository_id=None):
          
          if repository_id is None:
              raise NullArgument()
          if not self.supports_composition_admin() or not self.supports_visible_federation():
              raise Unimplemented()
          try:
              from . import sessions
          except ImportError:
              raise  # OperationFailed()
          try:
              session = sessions.CompositionSearchSession(repository_id,
                                                          proxy=self._proxy,
                                                          runtime=self._runtime)
          except AttributeError:
              raise  # OperationFailed()
          return session
docs: Gets a composiiton administrative session for the given
          repository.
  
          arg:    repository_id (osid.id.Id): the Id of the repository
          return: (osid.repository.CompositionAdminSession) - a
                  CompositionAdminSession
          raise:  NotFound - repository_id not found
          raise:  NullArgument - repository_id is null
          raise:  OperationFailed - unable to complete request
          raise:  Unimplemented - supports_composition_admin() or
                  supports_visible_federation() is false
          compliance: optional - This method must be implemented if
                      supports_composition_admin() and
                      supports_visible_federation() are true.