`message` in "runs" topic is not required but `null` is not accepted

[jakipatryk]

Describe the bug

Runs topic (https://github.com/AbsaOSS/EventGate/blob/master/conf/topic_runs.json) schema says that for each job in jobs, required properties are ["catalog_id", "status", "timestamp_start", "timestamp_end"]. So there is not message there. But when message is null in the body of POST /topics/public.cps.za.runs, the response is 400.

Expected behavior

null should be accepted as value of non-required fields, or message should be required (I think the former is better?).