diff --git a/depicts/type.py b/depicts/type.py
index 3418f47..0ce71b2 100644
--- a/depicts/type.py
+++ b/depicts/type.py
@@ -28,8 +28,8 @@ class Entity(TypedDict, total=False):
 class CatalogDict(TypedDict, total=False):
     """Catalog record from institution web site."""
 
-    institution: str
-    url: str
+    institution: str | None
+    url: str | None
     ids: set[str]
     detail: list[dict[str, str]]
     description: str
diff --git a/depicts/wd_catalog.py b/depicts/wd_catalog.py
index 22bfa8a..ca5b781 100644
--- a/depicts/wd_catalog.py
+++ b/depicts/wd_catalog.py
@@ -399,7 +399,6 @@ def get_catalog_from_artwork(entity: Entity) -> CatalogDict:
         catalog_detail.append(detail)
 
     url = wikibase.first_datavalue(entity, "P973")
-    assert isinstance(url, str)
     catalog: CatalogDict = {
         "url": url,
         "detail": catalog_detail,