Issues fixity check, return parsed graph

		Args:
			None

		Returns:
			(dict): ('verdict':(bool): verdict of fixity check, 'premis_graph':(rdflib.Graph): parsed PREMIS graph from check)

def fixity(self, response_format=None):

		'''
		Issues fixity check, return parsed graph

		Args:
			None

		Returns:
			(dict): ('verdict':(bool): verdict of fixity check, 'premis_graph':(rdflib.Graph): parsed PREMIS graph from check)
		'''

		# if no response_format, use default
		if not response_format:
			response_format = self.repo.default_serialization

		# issue GET request for fixity check
		response = self.repo.api.http_request('GET', '%s/fcr:fixity' % self.uri)

		# parse
		fixity_graph = self.repo.api.parse_rdf_payload(response.content, response.headers)

		# determine verdict
		for outcome in fixity_graph.objects(None, self.rdf.prefixes.premis.hasEventOutcome):
			if outcome.toPython() == 'SUCCESS':
				verdict = True
			else:
				verdict = False

		return {
			'verdict':verdict,
			'premis_graph':fixity_graph
		}