[BUGFIX] Don't skip schema validation for empty configurations
When performing a configuration validation via::
The validation was interrupted with an exception if one of the
parsed configuration types is empty (for example because no
``Views.yaml`` file existed).
This patch fixes the issue by replacing the exception with a
notice that can be outputted with the ``verbose`` flag.
Releases: master, 3.0, 2.3, 2.1