bug in Attached (fix after change 31470)

An attached property may be defined with mandatory=False.
In this case, when no value or an empty string is given,
<modobj>.<attached_mod> must return None after initialisation.

+ remove 'dispatcher' level from the logger hierarchy on modules

Change-Id: Icee3ae3f9142cd7a910c579ae1ffaa35f93cee03
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/32187
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

test/test_server.py

@@ -28,6 +28,9 @@ from .test_config import direc  # pylint: disable=unused-import
 
 
 class LoggerStub:
+    def __init__(self):
+        self.parent = self
+
     def debug(self, fmt, *args):
         pass