return apoc.convert.toJson({a:null}) as json_record_str;
throws an error, whereas it used to work perfectly before. This affects any JSON conversion for any object where there is a null value for any property. Per the JSON spec, null is a valid value: JSON
apoc.version() returns 4.4. Note I can't control the apoc version installed on Neo4J Aura, so all Aura users will be affected until either Apoc is rolled back or this is fixed in 4.4.