diff --git a/caldav/lib/url.py b/caldav/lib/url.py
index 0d61998..9feff4a 100644
--- a/caldav/lib/url.py
+++ b/caldav/lib/url.py
@@ -84,7 +84,7 @@ def __hash__(self) -> int:
     # object, else will instantiate a new URL object
     @classmethod
     def objectify(self, url: Union[Self, str, ParseResult, SplitResult]) -> "URL":
-        if isinstance(url, (URL, None)):
+        if url is None or isinstance(url, URL):
             return url
         else:
             return URL(url)