fix: a data value of 0 turns into {}

Don't use truthyness here, but since None would also be a valid
value, remove it entirely.

ipyvue/VueWidget.py

@@ -123,7 +123,7 @@ def _fire_event(self, event, data=None):
         dispatcher = self._event_handlers_map[event]
         # we don't call via the dispatcher, since that eats exceptions
         for callback in dispatcher.callbacks:
-            callback(self, event, data or {})
+            callback(self, event, data)
 
     def _handle_event(self, _, content, buffers):
         event = content.get("event", "")