rules: add checks for empty process name and class

docs/rules.md

@@ -5,7 +5,10 @@ layout: page
 
 Rule processing is an experimental feature.  Significant changes might be made in response to problems.
 
-Note that rule processing is only available when running under X11.
+Note that rule processing only fully works under X11.
+When running under Wayland with X11 libraries loaded most features will not be available and errors may result.
+Features known not to work under Wayland include process conditions and
+anything to do with simulating keyboard or mouse input.
 
 Logitech devices that use HID++ version 2.0 or greater produce feature-based
 notifications that Solaar can process using a simple rule language.  For

lib/logitech_receiver/diversion.py

@@ -340,7 +340,8 @@ class Process(Condition):
     def evaluate(self, feature, notification, device, status, last_result):
         if not isinstance(self.process, str):
             return False
-        return active_process_name.startswith(self.process) or active_wm_class_name.startswith(self.process)
+        return bool(active_process_name and active_process_name.startswith(self.process)) or \
+            bool(active_wm_class_name and active_wm_class_name.startswith(self.process))
 
     def data(self):
         return {'Process': str(self.process)}