feat(bug): defensive code to avoid accesing attribute of a NoneType object (#35219)

Author: gabotorresruiz

superset/dashboards/api.py

@@ -1342,6 +1342,8 @@ def thumbnail(self, pk: int, digest: str, **kwargs: Any) -> WerkzeugResponse:
         self.incr_stats("from_cache", self.thumbnail.__name__)
         try:
             image = cache_payload.get_image()
+            if not image or not hasattr(image, "read"):
+                return self.response_404()
         except ScreenshotImageNotAvailableException:
             return self.response_404()
         return Response(