[ML] Saved search using KQL with negation operator (NOT) returns a blank page on ML job creation

[ppf2]

Kibana version: Tested in both 7.6.0 and 7.7.1

Elasticsearch version: Same as Kibana

When creating a ML anomaly detection job from a saved search in Kibana, if the saved search contains a KQL that includes the "not" operator, e.g., NOT field_name:something, the job creation fails without any errors (in either ES or Kibana) and the page simply refreshes to a blank page without providing further options to proceed with the actual creation. If the saved search has just field_name:something, everything works. I haven't tested all the other operators, but a:b AND c:d also works.

Saved search: export (2).ndjson.zip

Workaround: Switch the default KQL query option back to the previous Lucene default:

[elasticmachine]

Pinging @elastic/ml-ui (:ml)