diff --git a/radicale/item/filter.py b/radicale/item/filter.py
index f69284ce..209bd1cb 100644
--- a/radicale/item/filter.py
+++ b/radicale/item/filter.py
@@ -274,7 +274,7 @@ def get_children(components: Iterable[vobject.base.Component]) -> Iterator[
             if hasattr(comp, "recurrence_id") and comp.recurrence_id.value:
                 recurrences.append(comp.recurrence_id.value)
                 if comp.rruleset:
-                    if comp.rruleset._len == None:
+                    if comp.rruleset._len is None:
                         logger.warning("Ignore empty RRULESET in item at RECURRENCE-ID with value '%s' and UID '%s'", comp.recurrence_id.value, comp.uid.value)
                     else:
                         # Prevent possible infinite loop