This works around an issue with Matrix Authentication Service's `syn2mas` sub-command (at version v0.16.0),
which chokes with an error:
> Error: Failed to load Synapse configuration
> Caused by:
> invalid type: found unit, expected struct EnableableSection for key "default.cas_config" in homeserver.yaml YAML file
This issue is likely to be fixed in MAS v0.16.1 or v0.17.0.