trivial: expand NullLogger

wcs/qommon/publisher.py

@@ -456,10 +456,14 @@ class QommonPublisher(Publisher):
             self._app_logger = self.get_app_logger(force = True)
         else:
             class NullLogger(object):
-                def error(*args): pass
-                def warn(*args): pass
-                def info(*args): pass
-                def debug(*args): pass
+                def error(self, *args):
+                    pass
+                def warn(self, *args):
+                    pass
+                def info(self, *args):
+                    pass
+                def debug(self, *args):
+                    pass
             self._app_logger = NullLogger()
 
     def set_app_dir(self, request):