Close #133. Don't attempt to display/render non-DOMWidget (i.e., Widget) objects

Author: cpsievert

shinywidgets/_render_widget_base.py

@@ -89,6 +89,10 @@ async def render(self) -> Jsonifiable | None:
 
         self._widget = cast(WidgetT, widget)
 
+        # Don't actually display anything unless this is a DOMWidget
+        if not isinstance(widget, DOMWidget):
+            return None
+
         return {
             "model_id": str(
                 cast(