diff --git a/radicale/storage/__init__.py b/radicale/storage/__init__.py
index 4e2e95dd..73cf77b9 100644
--- a/radicale/storage/__init__.py
+++ b/radicale/storage/__init__.py
@@ -27,7 +27,7 @@ import json
 import xml.etree.ElementTree as ET
 from hashlib import sha256
 from typing import (Callable, ContextManager, Iterable, Iterator, Mapping,
-                    Optional, Sequence, Set, Tuple, Union, cast, overload)
+                    Optional, Sequence, Set, Tuple, Union, overload)
 
 import vobject
 
@@ -283,9 +283,9 @@ class BaseStorage:
         self.configuration = configuration
 
     def discover(
-            self, path: str, depth: str = "0", 
+            self, path: str, depth: str = "0",
             child_context_manager: Optional[
-            Callable[[str, Optional[str]], ContextManager[None]]] = None, 
+            Callable[[str, Optional[str]], ContextManager[None]]] = None,
             user_groups: Set[str] = set([])) -> Iterable["types.CollectionOrItem"]:
         """Discover a list of collections under the given ``path``.
 
diff --git a/radicale/storage/multifilesystem/discover.py b/radicale/storage/multifilesystem/discover.py
index 5cff9789..a635906a 100644
--- a/radicale/storage/multifilesystem/discover.py
+++ b/radicale/storage/multifilesystem/discover.py
@@ -36,9 +36,9 @@ def _null_child_context_manager(path: str,
 class StoragePartDiscover(StorageBase):
 
     def discover(
-            self, path: str, depth: str = "0", 
+            self, path: str, depth: str = "0",
             child_context_manager: Optional[
-            Callable[[str, Optional[str]], ContextManager[None]]] = None, 
+            Callable[[str, Optional[str]], ContextManager[None]]] = None,
             user_groups: Set[str] = set([])
             ) -> Iterator[types.CollectionOrItem]:
         # assert isinstance(self, multifilesystem.Storage)