fix visualization_dataset id

Author: davidgamez

api/src/feeds/impl/models/gtfs_feed_impl.py

@@ -25,5 +25,7 @@ def from_orm(cls, feed: GtfsfeedOrm | None) -> GtfsFeed | None:
         gtfs_feed.locations = [LocationImpl.from_orm(item) for item in feed.locations]
         gtfs_feed.latest_dataset = LatestDatasetImpl.from_orm(feed.latest_dataset)
         gtfs_feed.bounding_box = BoundingBoxImpl.from_orm(feed.bounding_box)
-        gtfs_feed.visualization_dataset_id = feed.visualization_dataset_id
+        gtfs_feed.visualization_dataset_id = (
+            feed.visualization_dataset.stable_id if feed.visualization_dataset else None
+        )
         return gtfs_feed