Update

src/vitessce/widget.py

@@ -487,6 +487,7 @@ def __init__(self, config, height=600, theme='auto', uid=None, port=None, proxy=
         :param str custom_js_url: A URL to a JavaScript file to use (instead of 'vitessce' or '@vitessce/dev' NPM package).
         :param list[WidgetPlugin] plugins: A list of subclasses of VitesscePlugin. Optional.
         :param bool remount_on_uid_change: Passed to the remountOnUidChange prop of the <Vitessce/> React component. By default, True.
+        :param bool prefer_local: Should local data be preferred (only applies to `*_artifact` data objects)? By default, True.
         :param int invoke_timeout: The timeout in milliseconds for invoking Python functions from JavaScript. By default, 30000.
 
         .. code-block:: python

src/vitessce/wrappers.py

@@ -131,7 +131,7 @@ def try_getting_artifact_stores(self):
         artifact_stores = dict()
         for artifact_url, artifact in self.artifacts.items():
             local_path = artifact._local_filepath
-            if os.path.isdir(local_path):
+            if local_path is not None and os.path.isdir(local_path):
                 store = zarr.DirectoryStore(local_path)
                 artifact_stores[artifact_url] = store
         return artifact_stores