What is the bug?
The GetAlerts API throws a 404 NOT_FOUND error when there are no detectors for the specified detectorType.
https://github.com/opensearch-project/security-analytics/blob/main/src/main/java/org/opensearch/securityanalytics/transport/TransportGetAlertsAction.java#L126

This can cause a built-up of 4xx errors on clusters that make regular/repeated calls to that API.

What is the expected behavior?
Rather than throw an error, the GetAlerts API could be refactored to instead return an empty list when there are no detectors defined for the specified detectorType.