code: def oaiset(self):
          
          if current_app.config['COMMUNITIES_OAI_ENABLED']:
              from invenio_oaiserver.models import OAISet
              return OAISet.query.filter_by(spec=self.oaiset_spec).one()
          else:
              return None
docs: Return the corresponding OAISet for given community.
  
          If OAIServer is not installed this property will return None.
  
          :returns: returns OAISet object corresponding to this community.
          :rtype: `invenio_oaiserver.models.OAISet` or None