def get_by_id(self, id, change_notes=False):
        """ Get a :class:`skosprovider.skos.Concept` or :class:`skosprovider.skos.Collection` by id

        :param (str) id: integer id of the :class:`skosprovider.skos.Concept` or :class:`skosprovider.skos.Concept`
        :return: corresponding :class:`skosprovider.skos.Concept` or :class:`skosprovider.skos.Concept`.
            Returns None if non-existing id
        """
        graph = uri_to_graph('%s/%s.rdf' % (self.url, id), session=self.session)
        if graph is False:
            log.debug('Failed to retrieve data for %s/%s.rdf' % (self.url, id))
            return False
        # get the concept
        things = things_from_graph(graph, self.subclasses, self.concept_scheme)
        if len(things) == 0:
            return False
        c = things[0]
        return c