Checkmk Werk 15979: bi: return 404 status code when trying to retrieve a non existing rule

ID: 15979 Title: bi: return 404 status code when trying to retrieve a non existing rule Component: REST API Level: 1 Class: Bug fix Version: 2.0.0p38 Prior to this werk, the get bi rule endpoint returned a 500 status code whenever the user tried to get a non existing rule. This werk fixes this and returns a 404 status code instead.