[2.4.0] Checkmk Werk 16802 created: Synthetic monitoring: Fix crash in "Robotmk scheduler (Windows)" bakery rule when attempting to save with invalid settings

[//]: # (werk v2) # Synthetic monitoring: Fix crash in "Robotmk scheduler (Windows)" bakery rule when attempting to save with invalid settings key | value ---------- | --- date | 2024-04-24T12:38:16+00:00 version | 2.4.0b1 class | fix edition | cee component | setup level | 1 compatible | yes When attempting to save the bakery rule "Robotmk scheduler (Windows)" with invalid settings such as an empty base directory or an invalid application name, the UI page crashed with <code>TypeError: argument of type 'NoneType' is not iterable</code>.