Clarify exception message in EHFactoryBase

tfw/internals/event_handling/event_handler_factory_base.py

@@ -26,7 +26,7 @@ class EventHandlerBuilder:
     def _determine_type(self, provided_type):
         type_ = provided_type or self._analyzer.event_handler_type or EventHandler
         if not issubclass(type_, EventHandler):
-            raise ValueError("No type supplied!")
+            raise ValueError("Invalid type supplied!")
         return type_
 
     def build(self, connector):