rel_properties_query = '\nMATCH (
)-[r]->()\nWITH keys(r) as keys, type(r) AS types\nWITH CASE WHEN keys = [] THEN [NULL] ELSE keys END AS keys, types \nUNWIND types AS type\nUNWIND keys AS key WITH type,\ncollect(DISTINCT key
) AS keys \nRETURN {types:type, keys:keys} AS output\n'